Rhodium, and Iridium

From spectral and n.m.r. measurements it is apparent that the equilibrium 2[RhCl(PPh3)J [RhaQaCPPha)  

Chlorotris(triphenylphosphine)rhodium(i) can also catalyse hydrogen transfer from dioxan to an alkene. The rate-determining step in this reaction is considered to be oxidative addition of C—bonds of dioxan to the catalyst  

The stereochemistry of the addition of hydrogen to an olefinic double bond catalysed by [RhCl(PPh3)a] has been shown to involve cis addition, in agreement with earlier studies.  

Mitsui, H. Sugiyama, and S. Seto, Bull. Chem. Soc. Japan, 1972, 45, 3498. 

Neither of these reactions is observed in benzene but the polar iSW-dimethyl-acetamide assists dissociation of the octahedral complex and heterolysis of the hydrogen. Activation parameters for the reduction are A f = 12.9 kcal mol , = — 21 cal deg mol . The small isotope effect observed 

Rhodium and Iridium.—Ford16 has discussed the deficiencies of the ligand-field model for d9 systems14 when applied to RhUI photochemistry. In particular he criticizes (i) the neglect of possible variations in the efficiency of radiationless processes in estimating the relative quantum yields for the reactions of the photo-excited states and (ii) the use of crystal-field parameters derived from the ground-state configuration. 

Photo-exchange of water from [Rh(NH3)5H20]3+ in oxygen-18 enriched water proceeds efficiently on ligand-field excitation of the complex.107 In the presence of Cl- photo-anation (40) takes place. 

The first report of luminescence from a transition-metal exciplex has been published.108 In DMF solution the emission of c/j,-[Ir(phen)2Cl2]+ is quenched by naphthalene and replaced by a new structureless emission band at longer wavelengths. 

In aqueous solution m-[Ir(phen)2Cl2]+ undergoes Cl aquation (reaction 41) with a quantum yield of 0.05 independent of in the range 250—404 nm.109 On flash photolysis a transient species, which is not an intermediate in reaction (41), 

10-phenanthroline complexes of Rh111 and IrIM,113 and of phosphine complexes of Rh1 and Ir1,114 have been discussed. 

Rhodium and Iridium. - The spectrum of CO adsorbed on evaporated Rh films and Si02 or AI2O3-supported metal particles has been studied by many authors. For a detailed review, the reader is referred to that by Sheppard and Nguyen.In brief, an intense band around 2060 cm is caused by CO linearly adsorbed bridged species absorb in a wide range (1925-1780 cm ) a couple of bands at about 2100 and 2030 cm are related to dicarbonylic species formed on incompletely reduced metal sites [probably Rh (CO)2]. 

Numerous papers have appeared recently about Rh dispersed on oxide systems both via salt impregnation ° ° ° and via heterogenization of Rh carbonyls [basically Rh6(CO)i6 and Rh4(CO)i2] In the follow- 

Solymosi, A. Erdohelyi, and T. Bansagi, J. Chem. Soc., Faraday Trans. 1, 1981, 

Bilhou, V. Biihou-Bougnol, and W. F. Graydon, Inorg. Chem., 1979, 18, 3104. 

on Catalysis, Tokyo, 1980, ed. T. Seiyama and K. Tanabe, Elsevier, 

Rhodium and Iridium. Tetracyanoethylene, TCNE, undergoes reversible addition to rhodium complexes as in equation (45), where X=C1, L=P(4-MeOC H4)8, 

P(4-MeCeH4)3, PPha, P(4-ClC6H4)s, PMePha, AsPhj, P(0-2-MeC.H4)3, or P(OPh 3 X=Br, I, NCO, or NCS, L=PPha. Similar reactions occur with lRhCl(CS)-(PPhala] and rra j-[IrCl(CO)(PPh3)a] and in all cases studied the kinetics were found to obey rate law (46) for a reversible reaction, where and k-x are the forward 

8 Rhodium and Iridium.- Cyclopentadienyl stabilised dirhodium complexes include the 

8 Rhodium and Iridium. - Complex [Ir2 Tcbiim)2(CO)2(lfeCH)2 P(OEt)3 2] (H2Tcbilm = tetracyanobiimldazole) contains an unbridged Ir-Ir bond 2.826(2)A. Vibrational and electronic spectra of isocyanide bridged Rh(Il) and ir(Il) c( q lexes [M2(c/1jc)4L2] have been analysed.  

Cxrystal structures are reported for (Rh2(ifC0) f (C5H4)2CH2 (C0)2] 

Alkali metal reduction of [Rh2(g-C0)2Cp2l 0) generates anions with 

Additions of activated alkynes to [Ir2(x pa)2(cod)2] afford parallel ( t-c,o-RCCR) bridged produots. [Rh2 x PB)2(C0)2 PPh2(o-BrCgP4) 2] undergoes a thermal ortho-metallatlon to fora tRh2(M pa)2(/ -Ph2PC5P4)Br C0)- 

Bie geonetric isonerisatlons occurring for [Bb( FBu 2(C0)4] as a neutral entity and during its reversible reduction to structurally characterised 

8 Rhodium and Iridium. - The stericaily crowded complex [Rh2 i-(Me2 2 2 PMe)2(C0)2l2 has a structure in which a six co-ordinate Rh atom completes the 

Cyclooctatetraene adopts two different bridge-bonding modes in dlrhodium complexes [Rh2 it-n in -cot (i7 -nbd Cp] and [Rh2 k-l,2,6-)7 3-5-n-cot Cp2].27  

The redox properties of species [Rh2(ti-flC2R)(u-CO)Cp2J (R - Bu, CF- ) have been investigated cations (2+ and l+ and anions (l- are observed and the monocation (R = Bu is very stable.2 2 Reactions of [Rh2(tf-CF3C2CF3 ( t-C0 -CP2I with alkenes and with alkynes are reported alkenes react by hydrogen 

A number of new trinuclear complexes of Rh3 or Ir3 bridged by two triphosphine or diphosphine-arsine ligands (Ph2PCH2)2EPh E - Pj As (dpma) possess one metal-metal interaction289a structurally characterised 

Clusters [Ir4(C0)j j L) (L - phosphine, arsine, alkene, SO2) and [Ir4(CO)ioL2l L2 = dlphosphine, n -polyalkene) may be synthesised from [Ir4(C0)iiBr]T 293 Anions [Irg(M-CO)4 CO)jj COOR)] are formed from attack of (IrglCOlj g) by NaOR.294 

The spectrum of trivalent rhodium has been reported in the LiCI-KCl 

TABLE XLIII. Spectral Results for Rh(III) in LiCl-KCl Melt and Aqueous HCl 

It was suggested that in the nitrate melt the rhodium species was Rh(N02)6 in which nitro coordination was present. With the addition of KCl, pronounced spectral changes were observed until, at a mole ratio of RhCl3 KCl of 1 600, the spectrum contained two bands, at 18.8 and 24 kK, which were almost certainly due to the RhCl species. 

In the ternary sulfate melt the spectrum of Rh(III) contains a single band at 21 kK (e — 150) together with the low-energy edge of a charge transfer band (Fig. 44). comparison of Fig. 43 and 44 led us to expect 

The spectrum of Ir(III) in the LiCl-KCl eutectic melt has been shown to contain four bands (Fig. 45).(262,263) jable XLIV lists the band maxima and extinction coefficients for both the LiCl-KCl melt and an aqueous HCl solution of IrCli . The similarity between the two results suggests that 

No reactions of complexes 62 and 63 have been reported. Palladium and platinum form no well-defined dinitrogen complexes. However, until relatively recently there were few carbonyl complexes of palladium and platinum. This has changed rapidly with the preparation of a wide variety of compounds such as dinuclear complexes, e.g., [M2Cl2(ju,-CO)-(ju. -dppm)2] where M = Pd, Pt, and neutral and anionic polynuclear complexes such as [Os2(CO)6 /t-Pt-(CO)(PPh3) 2] and [Pt9(CO)i8]. The absence of simple, mononuclear palladium and platinum dinitrogen complexes should not be construed as evidence that this is a barren area for research. 

These results have been successfully reproduced in one other labora-tory/ Unfortunately, the crucial experiment using and analyzing for has not been carried out yet. 

Under CO [Rh(CO)2Cl2], dppm, and NapPh4] yield [Rh2(CO)2(A -CO)0M-Cl)CM-dppm)2][BPh4] from which one carbonyl ligand is readily lost. The decarbonylated product reacts with SO2 to give [Rh2(CO)20 -SO2)(/t-Q)0M-dppm)2]+, and subsequently [RhjCUCM-SOaX/t-dppmla]. 

Hfb and [Rh(CO)2L] [L = dipivaloylmethanato) give (42) in which the bridging acetylene is almost parallel to the metal-metal bond.  

Dwight, and A. R. Sanger, Inorg. Chim. Acta, 1978,31, L407. 

M2 units bridged by nitrogen ligands include [Rh2(u-napy)j(nbd)2 (napy = 1,8-naphthyridine) [Rh (ii-az) 2 (u Cl) 2 (p-CO) 2 (CO) 2 (nbd) 2 (Haz = 7-azaindole),with two directly bonded Rh2 units in a planar Rh Cl2 framework Clr2 (p-pz) (y PPh2) (cod) (CgHj )  

B-ddazoketones also yield a-alkylidenes or bridging ligands incorpor- 

Full details of Rh(IV) complexes derived from [ Rh2(y-CH2)2Me2Cp 3 

C0) which exhibit intramolecular alkyl migration, and di-substituted species [ Rh2 (y-CH2) 2l 2 P2 both complex types form 

Structures reported for open trinuclear complexes bridged by triphosphines are CRh3 w3-PhP(CH2PPh2)2 2 ( - 0)2 (w-SjCOEt) (CO) (S2C0Et) 3 and CRh, u,-PhP(CH2PPh2)5, (v,-lXu-I),I(CO)3 258b 

When a deuteriated ethyl derivative (R = CH2CD3) was studied only CH2=CD2 was detected, which sug ts that Ni—C bond fission in the proposed diethylnickel intermediate proceeds through a jff-hydride elimination mechanism. 

Cobalt, Rhodium, and Iridium.— Reaction of pentafluorophenylmagnesium bromide with CoBra in THF apparently yields bis(pentafluorophenyl)cobalt, which is stable in THF solution but cannot be isolated as such. However, addition of tri-n-butylphosphine yields the stable complex [(Bu sP)2Co(C6Fb)2], also available by reaction of CeFgMgBr with (Bu aP)2CoBr2. Bis(pentafluorophenyl)cobalt yields pentafluorobenzene with water, with oxygen yields perfluorobiphenyl (69%) and theperfluoro- 

Reaction of bis(pentafluorophenyl)acetylene with the rhodium complex [(Tr-CsHjIRhfCO) ] in refluxing toluene or xylene yields hexakis(pentafluoro-phenyl)benzene (40—70%), together with several rhodium complexes including [(7r-C5H5)3Rh3(CO)(C,F -C C-C,Fj)] and the cyclopentadienone complex (222).  

Oxidative addition of pentafluorobenzoyl chloride to the nitrogen complex tra/ij-[(Ph5P)2lr(Ng)a] yields the pentafluorophenyl complex (223).  

During a study of electronic effects of pseudo-halo ligands, the complex trflKJ-[(Ph2PMe)jPd(C F5)(NCS)] was prepared from the corresponding chloro-complex and NaNCS in acetone.  

Cobalt, Rhodium, and Iridium.—Much work has been published during the period covered by this Report concerning oxidative addition reactions of complexes of rhodium and iridium, particularly those of the d type. 

Tetrafluoroethylene reacts with octacarbonyldicobalt to give initially the cr-complex (125), which loses CO when heated in vacuo to give the fx,- 

The complete series of trifluoiophosphine complexes RfCo(CO)x(PF3)4-z (Rp = CF3, CjFg, or n-CjFg) has been prepared by reaction of PF3 with the acyl complexes RfCO-Co(CO)4. There is evidence of the presence of a mixture of stereoisomers from the i.r. spectra, and the low-temperature F n.m.r. spectrum of CFg-CofCOlafPFj) shows the presence of two isomers of 

and their co-workers have studied extensively the reactions of unsaturated electrophilic reagents, such as fluoro-olefins, acetylenes, ketones, etc., with f complexes, but the rather delicate factors which control the type of reaction shown are, as yet, only partially understood. 

The complex [(acac)Rh(PhjPMe)2] reacts with tetrafluoroethylene and chlorotrifluoroethylene to yield the rhodacyclopentane complexes (131), but with bromotrifluoroethylene, complex (132) is formed. In the reaction with 1,2-dichlorotetrafluorocyclobutene, transfer of chlorine to metal occurs, giving the vinylic complex (133). The complex [(acac)Rh(Ph2PMe)j] reacts with only one mole of hexafluoroacetone, yielding (134), but with the corre- 

External magnetic field effects on the excited state properties of Rh(l) and Ir(I) complexes have been discussed. 

A crystal-structure determination reveals a trihapto allyl co-ordination for the dienyl ligand in (cod)Rh(j -cyclo-octadienyl), giving the Rh a 16 electron configuration. The i -benzyl complex (38) has been prepared. Styrene dissociation occurs in solution, and while an exchange process results in equivalence of the two ortho protons, the steric environment at the ben2yl carbon remains constant. This is shown to occur by a selective antarafacial rearrangement via an -benzyl intermediate.  

Rhodium is the element of the big clusters, Gorrespondingly, relatively few clusters are known with three and four rhodium atoms, but there is a rich chemistry from hexanuclear complexes upward. 

Among the trirhodium systems, the well-known Gp3Rh3(GO)2 reacts with tri-methylsilyl azide to form (GpRh)(u3 NSiMe3) with a structure like 

Two syntheses of Rh4(CO)i2 at ordinary pressure have been developed 81, 279 making this compound easily available, and CO scrambling in this molecule has been carefully examined 110,112,164. Strong nucleophiles including CO at high pressure destroy the Rh cluster 45, 396, but with phosphines of limited donor strength, with cyclooctatetraene, and with acetylenes up to four CO groups could be replaced with retention of the Rh4 unit 45, 247, 396. Rh4-like Rhg-clusters show catalytic activity (7 04, 364 which has been used for hydroformylation 88 and oxidation (297) reactions. 

From 1-6 M HCl, containing SnCF, rhodium(III) can be separated from Ir, Pd, and Pt by extraction with benzene in the presence of DAPM [1], TOA [2,3], or 2-octylaminopyridine [4]. Rhodium is also extracted with isoamyl alcohol from an acid medium containing bromide and Sn(II) after heating at 90°C [5]. 

From a 0.06 M HCl medium hexachloroiridate(IV) can be extracted as an ion-pair with tetraphenylarsonium cation [6]. This method enables one to separate Ir from Rh and Pd, but not from Pt. Ir has been separated from Rh, also, by extraction with tetra-n-butylammonium ion [7]. 

Rh (also Ir, Pd, and Pt) can be extracted with bis-(2-ethylhexyl)dithiophosphoric acid [8]. Ir can be extracted with mercaptobenzothiazole [9] or thiobenzanilide [ 10]. Rhodium has been separated from Ir by the extraction (CHCI3) of its complex with 2-mercaptobenzimidazole [11]. HDEHP has been used for extraction separation of Rh from Ru and Ir [12]. Extraction of Rh (and other noble metals) by thiourea and its derivatives was studied [13]. 

Rhodium(III) can exist as a cationic complex in hydrochloric acid medium, whereas Ir(IV), Pt(IV), and Pd(II) exist as anionic complexes. These properties enable their separation with the use of ion exchangers [14-16]. 

Chelate complexes of Rh with TAR [17,18], TAN [19], PAN [20-22], and 8-hydroxyquinoline [23] and its derivatives [24] have been used for separation of Rh by the liquid chromatography. 

Kolwaite, E. Rosenberg, K. Hardcastle, J. Ciurash, R. Duque, R. Gobetto, L. Milone, D. Osella, M. Botta, W. Dastru, A. Viale, and I. Fiedler, 

Kadyrov, D. Heller, W. Baumann, A. Spannenberg, R. Kempe, J. Holz, and A. Bomer, ar. J. Irurrg. Chem., 1998,1291. 

Fawcett, S. Friedrichs, J.H. Holloway, E.G. Hope, V. McKee, M. Nieuwenhuyzen, 

Rhodium was discovered in 1803 by the eminent Norfolk scientist W.H. Wollaston he dissolved platinum metal concentrates in aqua regia and found that on removing platinum and palladium he was left with a red solution. From this he obtained the salt Na3RhCl6, which yielded the metal on reduction with hydrogen. The rose-red colour (Greek rhodon) of many rhodium salts gave the element its name. 

Trinuclear and Larger Clusters - Addition of sodium sulfide to [Cp M(MeCN)3] yields sulfido-capped [Cp 3M3(p -S)2l (M=Rh,Ir), the iridium complex also being isolated from 

Palladium - Two papers describe the preparation of diphosphine complexes [Pd2(il -diphoshine)2(p-H)(p-CO)] 0,351 carbonylation of [Pd(T] -allyl)(p-Cl)J2 in the presence of PPh3 yields trinuclear complexes [Pd3(PPh3)j,(p-CO)3] (n=3,4), and addition of XyNC (Xy=2,6-Me2CgH3) to [Pd3(p-dppm)3(p -CO)] affords [Pd3(p-dppm)3(p -ri -CNXy)]  

Platinum- Anderson and coworkers have described the synthesis and reactivity of the Pt(I) dimer [Pt(CO)(p- n -l,l-C5H4PPh2)]2 (43) and also the preparation of the datively-bonded Pt(II) 

Compounds uith Heteronuclear Transition Metal Bonds 

Due to a the limitation of space a discussion of individual publications in this section is not feasible. Hence fOT both binuclear and polynuclear complexes, lists of relevant examples will be given (lightest atom first) followed by a brief discussion of those examples which, in the authors opinion, represent the more interesting and novel reports. 

Both isomers, 180 (M = Ir, R = R = Me, R = R = H) and 181, react with Fe(CO)5, Fc2(CO)9, andFc3(CO)L2 to form a wide variety of products (91JA2544). In 186, 2,5-dimethylthiophene fulfills a bridging function maintaining its -q-coordination to the iridium site and coordinating in an ti -(S) fashion to the Fe(CO)4 group. This is an example of the V TiVS)-p,2-coordination mode. In 187, the 

Reaction of 180 (M = Rh, R = R = r = R = Me) with dry oxygen occurs via the sulfur atom to yield the 5-oxide complex 202 (M = Rh) (90JA2432,92JA8521). A species similar to 202 (C5Mc4H instead of Cp ) is formed in the base hydrolysis 

R = R = Me) (890M2739), in the solid state slowly rearranges into a species with amixed coordination mode, 205 (92JA1732). Solutions of 205 on interacting with air give the S-oxide, [Cp Rh(Ti -C4Mc4SO)] (90JA2432). 

As mentioned earlier, the possible products of the -complexes include ring-opened structures. This includes isomer 181 and some of its derivatives, for example, 187,188,196,197, 203, and 204, as well as the products of interaction with organoiron, 180,191, and 194, and organocobalt, 199,200, and 201, compounds. They have already been discussed together with the variously characterized V-complexes. Examples of the ring-opening reactions based on the -q- and ri -species are given next. 

Chemical reduction of 177 by dicyclopentadienyl cobalt is different from that of a thiophene derivative and leads to the removal of a heteroatom to yield 213. The latter reacts with tellurophene and Fc3(CO)l2 to give 214 [97JCS(D)1579]. 

Carbonylation of benzene to benzaldehyde has been achieved with IrBr(CO) (dppe) (dppe-Ph PCH CH PPh ), 

The chemistry of the [Co(CN)s] is by no means always restricted to the monomeric unit. H2/D2 studies indicate that the addition of H2 to this species is heterolytic involving a dicobalt species containing not a Co-Co bond but a CoNCCo unit reactions (84)-(88) are suggested.  

The oxidative addition of methyliodide to trans-[RhCl(CO)(PR3)2] is more complicated than previously supposed/ When R is Bu , /1-C8H17, or n-Ci8H37, the product is the expected Rh(III) complex, as in equation (89) rate constants are approximately equal. However when R is triaryl, the expected oxidative addition still occurs, but it is complicated by insertion 

A novel form of the oxidative addition/reduction elimination process has been observed which involves transfer of two chloro groups from one metal center to another, namely, Rh or Ir to Rh, Ir or Pt, as in equation (91) (L = PMe2Ph or PEt2Ph) in which a double-bridged intermediate is postulated.  

The first step in the thermal decomposition of the metallocycloalkane complexes [CpM(CH2) (PPh3)] (M = Rh or Ir = 4,5,6) is decomposition of the alkane ring with the formation chiefly of alkenes. Activation energies are about 35 and 70kcalmor for the rhodium and iridium compounds, respectively. 

Reductive elimination from rhodium complexes containing cr-bonded unsaturated acyl groups, e.g., [RhCH=CHR(CO)(PPh3)2Cl2], gives not the expected RCH=CHC1 but RCH=CHPPh3. The observed rate law 

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R. S. Dickson, Homogeneous Catalysis with Compounds of Rhodium and Iridium, Reidel, Dordrecht, The Netherlands, 1985. 

The platinum-group metals (PGMs), which consist of six elements in Groups 8— 10 (VIII) of the Periodic Table, are often found collectively in nature. They are mthenium, Ru rhodium, Rh and palladium, Pd, atomic numbers 44 to 46, and osmium. Os indium, Ir and platinum, Pt, atomic numbers 76 to 78. Corresponding members of each triad have similar properties, eg, palladium and platinum are both ductile metals and form active catalysts. Rhodium and iridium are both characterized by resistance to oxidation and chemical attack (see Platinum-GROUP metals, compounds). 

High Temperature Properties. There are marked differences in the abihty of PGMs to resist high temperature oxidation. Many technological appHcations, particularly in the form of platinum-based alloys, arise from the resistance of platinum, rhodium, and iridium to oxidation at high temperatures. Osmium and mthenium are not used in oxidation-resistant appHcations owing to the formation of volatile oxides. High temperature oxidation behavior is summarized in Table 4. 

For tetranuclear cluster complexes, three stmcture types are observed tetrahedral open tetrahedral (butterfly) or square planar, for typical total valence electron counts of 60, 62, and 64, respectively. The earliest tetracarbonyl cluster complexes known were Co4(CO)22, and the rhodium and iridium analogues. The... 

The stereospecific polymerization of alkenes is catalyzed by coordination compounds such as Ziegler-Natta catalysts, which are heterogeneous TiCl —AI alkyl complexes. Cobalt carbonyl is a catalyst for the polymerization of monoepoxides several rhodium and iridium coordination compounds... 

Rhodium and iridium are exceedingly rare elements, comprising only 0.0001 and 0.001 ppm of the earth s crust respectively, and even... 

More than 200 ores are known to contain cobalt but only a few are of commercial value. The more important are arsenides and sulfides such as smaltite, C0AS2, cobaltite (or cobalt glance), CoAsS, and linnaeite, C03S4. These are invariably associated with nickel, and often also with copper and lead, and it is usually obtained as a byproduct or coproduct in the recovery of these metals. The world s major sources of cobalt are the African continent and Canada with smaller reserves in Australia and the former USSR. All the platinum metals are generally associated with each other and rhodium and iridium therefore occur wherever the other platinum metals are found. However, the relative proportions of the individual metals are by no means constant and the more important sources of rhodium are the nickel-copper-sulfide ores found in South Africa and in Sudbury, Canada, which contain about 0.1% Rh. Iridium is usually obtained from native osmiridium (Ir 50%) or iridiosmium (Ir 70%) found chiefiy in Alaska as well as South Africa. 

The metals are lustrous and silvery with, in the case of cobalt, a bluish tinge. Rhodium and iridium are both hard, cobalt less so but still appreciably harder than iron. Rhodium and Ir have fee structures, the first elements in the transition series to do so this is in keeping... 

Table 26.1 Some properties of the elements cobalt, rhodium and iridium...

R. S. Dickson, Organometallic Chemistry of Rhodium and Iridium, Academic Press, New York, 1983, 432 pp. C. White, Organometallic Compounds of Cobalt, Rhodium and Iridium, Chapman Hall, London 1985, 296 pp. 

The most stable carbonyls of rhodium and iridium are respectively red and yellow solids of the form [M4(CO)i2] which are obtained by heating MCI3 with copper metal under about 200 atm of CO. The black cobalt analogue is more simply obtained by heating [Co2(CO)g] in an inert atmosphere... 

Cases of the S-coordinated rhodium and iridium are quite scarce. To complete the picture, we next consider the possibilities of S-coordination using complicated derivatives of thiophene. 2,5-[Bis(2-diphenylphosphino)ethyl]thiophene is known to contain three potential donor sites, two phosphorus atoms and the sulfur heteroatom, the latter being a rather nucleophilic center (93IC5652). A more typical situation is coordination via the phosphorus sites. It is also observed in the product of the reaction of 2,5-bis[3-(diphenylphosphino)propyl]thiophene (L) with the species obtained after treatment of [(cod)Rh(acac)] with perchloric acid (95IC365). Carbonylation of [Rh(cod)L][C104]) thus prepared yields 237. Decarbonylation of 237 gives a mixture of 238 and the S-coordinated species 239. Complete decarbonylation gives 240, where the heterocycle is -coordinated. The cycle of carbonylation decarbonylation is reversible. 

The rhodium and iridium complexes of dibenzothiophene (L) reveal an interesting case of linkage isomerism (91IC5046). Thus, the ti S) coordinated species [MCp LCb] on thermolysis with silver tetrafluoroborate afford the Ti -coordinated dicationic species. 

Reaction of the cyclopentadienyl rhodium and iridium tris(acetone) complexes with indole leads to the species 118 (M = Rh, Ir) [77JCS(D)1654 79JCS(D)1531]. None of these compounds deprotonates easily in acetone, but the iridium complex loses a proton in reaction with bases (Na2C03 in water, r-BuOK in acetone) to form the ri -indolyl complex 119. This reaction is easily reversed in the presence of small amounts of trifluoroacetic acid. 

Organometallic chemistry of pyrrole is characterized by a delicate balance of the ti N)- and -coordination modes. Azacymantrene is an illustration of the considerable nucleophilicity of the heteroatom. However, azaferrocene can be alkylated at C2 and C3 sites. Ruthenium and osmium, rhodium, and iridium chemistry revealed the bridging function of pyrroles, including zwitterionic and pyrrolyne complex formation. The ti (CC) coordination of osmium(2- -) allows versatile derivatizations of the heteroring. 

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