Phosphine complexes of osmium

Allyl hydride complexes of osmium are isolated from treatment of phosphine-substituted osmacyclobutane complex 114 with a thallium salt (Scheme 21). The reaction initially provides a mixture of an unstable -benzyl hydride complex 115 and the rf -allyl hydride complex 116 the -benzyl intermediate ultimately isomerizes to the latter complex, a very rare instance of isolable allylic hydride products generated from a starting metallacyclobutane <2004OM4858>. 

There are now a substantial number of nitrido complexes of osmium(VI) and osmium(IV) as well as the osmiamate ion [OsVII 03N]. In addition to the ammine and ethylenediamine complexes, much recent work has been carried out on the bipy, phen and terpy complexes, often in connection with research into the photodissociation of water. The nitrosyl chemistry of the element, though seemingly not as extensive as that of ruthenium, has received much attention, and there has been considerable work on the phosphine, arsine and stibine complexes. 

We consider here the remarkably small number of complexes of osmium with primary and aromatic amines RNH2 all these involve phosphines as coligands. For complexes of pyridine and its analogues see p. 533 complexes of polydentate amines are considered in the sections which follow this one (p. 534). 

It is a singular circumstance that the known chemistry of the tertiary phosphite complexes of osmium differs quite significantly from that of the tertiary phosphines, arsines and stibines. The closest analogue to P(OR)3 in osmium coordination chemistry would seem to be PF3, but even here the similarities are not marked. The oxidation states found are 0, II, III and IV (there are no established zerovalent unsubstituted osmium phosphine complexes), and the phosphites form unsubstituted species of the type OsL and [OsL ] " which have no counterparts in phosphine chemistry. The reason for these differences must be associated in part at least with the different cone angles and basicities of P(OR)3 ligands as against PR3. Further similarities and differences between the chemistries of osmium phosphines, phosphites and phosphorus trihalide complexes would obviously constitute a worthwhile study. 

For this triad, only iron (Table 4.17) gives homoleptic complexes containing (tM — C bonds. The remaining elements form heteroleptic compounds. The stability of phosphine complexes of the type M(aryl)2 (PR3)2 decreases considerably according to the series Ni>Co>Fe. Ruthenium and osmium complexes characteristically activate the C —H bond in coordinated ligands and form compounds with (tM—C bonds as a result of oxidative addition. The following reactions serve as examples ... 

Unlike the above example, the majority of five-coordinate complexes appear to undergo oxidative-addition reactions in two separate steps. Additions to the bis phosphine complexes of ruthenium(O) (36) and osmium(O) (39) (XIV) are the most thoroughly studied examples of this generalization (see Section IV). The configurations of these complexes have been established by infrared spectroscopy and, in the case of the osmium complex, by X-ray diffraction (72), Addition of an electrophile A" " (for example H+, HgX+, or Br+ from Br2) to the five-coordinate complexes... 

Ruthenium(III), d, is ruthenium s most stable oxidation state and resembles rhodium(III) and iridium(III) more than osmium(III). The salts inelude the halides, hydroxides, and oxides RuCls SHaO is most important because it is a good starting material for other compounds and reacts readily with olefins and phosphines. Complexes of this oxidation state are known with water, eyanide, oxygenated organies, sueh as diketones and earboxylates, pyridines, earbonyls, ey-elopentadienyls, phosphine, and arsine ligands. A notable differenee between ruthenium(II) and ruthenium(III) is the absenee of ruthenium(III) nitrosyl complexes. 

Access to unsaturated ruthenium complexes has been achieved via phosphine complexation with triphenylborane. The synthesis and structure of the zwit-terionic arene complex (riCph-BPh2H)Ru(PMe3)2(SiMe3) is reported. A base-stabilised terminal borylene complex of osmium has been derived from reaction between a dichloroboryl complex and 8-aminoquinoline. ... 

Within the osmium complexes in oxidation states (II-IV) [11,12] the stability of the +4 oxidation state becomes more important. Ammine and tertiary phosphine complexes have been selected for detailed examination. 

Figure 1.60 Syntheses of some osmium complexes of tertiary phosphines.

Considerable structural information is available on osmium complexes of tertiary phosphines, arsines and stibines (Table 1.13) [152, 157]. 

Considerable structural information is available on osmium complexes of tertiary phosphines, arsines and stibines (Table 1.13) [152, 157], Comparison with data (mainly obtained from EXAFS measurements) on osmium diarsine complexes (Table 1.14) shows that as the oxidation state increases, osmium-halogen bonds shorten whereas Os-P and Os-As bonds lengthen. Bond shortening is predicted for bonds with ionic character,... 

Phosphine complexes, osmium, 19 642 Phosphine coordination complexes, of uranium, 25 436 Phosphine derivatives, 19 28 Phosphine oxide(s), 11 495-496 19 66 predicted deviations from Raoult s law based on hydrogen-bonding interactions, 8 814t in salicylic acid manufacture, 22 8 Phosphine oxide diols/triols, 11 501 Phosphine selenides, 22 90 Phosphinic acid, 19 20, 54-55 Phosphinic anhydride, 11 499 Phosphinothricin acetyltransferase (PAT) proteins, 13 360 Phosphite esters, 19 20 Phosphites, in VDC polymer stabilization, 25 720... 

Ru3(CO)10(Ph2C2)2, and Ru3(CO)9(C2(Ph)2)3 (128). The dinuclear complex Ru2(CO)6(C2Ph2)2, containing a metallocyclopentadiene ring similar to that observed for both iron and osmium, is a further product in the reaction this does imply very similar structures for the trinuclear adducts to those observed for iron and osmium. The carbonyl reacts with tetracyclone to yield the complex Ru3(CO)i0(C2Ph2)2, which may be related to the osmium compounds discussed later. Phosphine substitution of the carbonyls in some of these compounds has been established. 

Ruthenium(IV) and osmium(IV) phosphoraniminato complexes are formed by nucleophilic attack of phosphines on the nitrido ligand of ruthenium(VI) or osmium(VI). The first examples of this type of complexes are [Os (NPR3)(PR3)2(Cl)3] and [Ru (NPEt2Ph)(Cl)3(PEt2Ph)2], which have been documented in CCC (1987). While there are quite a few osmium complexes of this class, there appears to be only one structurally characterized ruthenium complex. 

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