Molybdenum tricarbonyl complexes

In recent work, Ashe et al. have prepared a series of molybdenum tricarbonyl complexes of C6H6B-R ligands.142 X-ray diffraction data on [H6C6B-N(CHMe2)2]Mo(CO)3 123 revealed that the metal is coordinated to the six ring carbons but not to boron. 

Cool the Schlenk tube under argon down to -78°C (dry ice-isopropanol slush bath), and then admit the tube to a vacuum (c. 0.1 mmHg). Pump for 60 s, then admit argon gas and allow the apparatus to warm up to room temperature. Repeat this freeze-thaw process twice more. Heat the stirred mixture at 160°C under argon for 2 h. An abundant yellow precipitate of the molybdenum tricarbonyl complex develops. 

Reactions of B-Substituted Borepin Molybdenum Tricarbonyl Complexes 1045... 

This is believed to occiu- by intercalation of the positively charged phenanthridinium iinit, and it is noted that this occurs 50 times more effectively at the electron-rich C and G bases than at the AT sites. Ligand 46 was prepared by reaction of the acid chloride form of the pendant 61) to the molybdenum tricarbonyl complex of cyclen (62). The monosubstituted cyclen was then reacted with 3 moles of (R)-or (S)-JV-(2-chloroethanoyl)-2-phenylethylamine (61). Quartemization was achieved by reaction of methyl iodide with the Eu(III) complex (61). 

Both silver nitrate and molybdenum hexacarbonyl react with the nine-membered ring system m,m,m-cyclonona-l,4,7-triene to form complexes of the types (C9Hi2)-3 AgN03 and C9Hi2Mo(CO)3, respectively (2S8). In the assigned structures, based on NMR and related data, the silver nitrate complex has the silver ions associated with the outertt-orbital lobes (XLIII), while the molybdenum tricarbonyl complex has the molybdenum bonded to the inner 7r-orbital lobes (XLIV). In both complexes, a crown conformation of the ligand is assumed. 

Diphenyl(phenylthiolato)antimony, PhjSbSPh, forms an octahedral molybdenum tricarbonyl complex. Mo(CO)3(Ph2SbSPh), with/ac-geometry and the ligands attached via antimony atoms (mean Sb—Mo 2.74 A, Sb—Mo—Sb 91.6-93.3°) rather than sulphur . Antimony-sulphur distances (mean 2.43 A) are normal. 

Detailed vibrational assignments have been carried out on arene chromium and arene molybdenum tricarbonyl complexes (18, 19). Splitting of the E band in the carbonyl region was observed for substituted benzene chromium tricarbonyl complexes but not in (CgHg)Cr(CO)3 itself, showing that the concept of local symmetry (Cg ) is of very restricted validity when discussing the C—O stretching vibrations in such complexes (18). 

Some reports of failures to obtain cyclobutadiene complexes have also appeared (10,40). Chatt et al. (21) also noted that biphenylene (II) was very reluctant to form a metal complex. The only ones which could be made were molybdenum tricarbonyl complexes where the Mo(CO)3 group was bonded to the benzene, rather than to the four-membered ring. 

Lynam and co-workers prepared a series of cyclopentadienyl molybdenum tricarbonyl complexes with varying allq nyl ligands. The synthesis... 

It is clear that [3 + 2] cyeloaddition chemistiy and Sonagashira eross-coupling reactions are powerful tools for the development of more complex CO-RMs and indeed other pharmaceutieals agents. Onee a suitable CO-RM has been developed there are thousands of possible interesting structures that ean then be attached on to the CO-releasing moeity. The cyclopentadienyl molybdenum tricarbonyl complexes shown in Scheme 3 could also be easily modified to give a eomplex with a terminal alkyne funetionality which would allow the same sort of chemistry to be carried out on those too. 

Complexation of metals to preformed polymers is a useful methodology for the synthesis of polymers incorporating metals into their backbones or sidechains. In 1984 the complexation of a molybdenum tricarbonyl complex to approximately 25% of the arenes in polyparaphenylene (PPP), was reported. This polymer displayed shifts in its IR spectrum similar to that of potassium-doped PPP. 

Few examples have been reported of metals coordinated to six-membered boron-sulfur heterocycles. Ashe et al. prepared 4-methyl-l,4-thiaborin (SC4H4BMe) which forms a stable molybdenum tricarbonyl sandwich complex 144.158 jn g etjert s laboratory, the reaction of the diborolyl complex 33 (Section 3.01.3.2) with COS afforded the dinuclear complex 145 whose structure was determined crystallographically.36 Other products, not involving boron-sulfur heterocycles and hence outside the scope of this discussion, were obtained via the treatment of 33 with different sulfur reagents such as CS2.36... 

Hunt s group (50, 51) have pioneered the application of the Cl source to organometallics such as the iron tricarbonyl complex of heptafulvene, whose electron impact spectrum shows (M—CO)+ as the heaviest ion, in contrast to the methane Cl spectrum with the ion as base peak. Boron hydrides (52) and borazine (53) have also been studied. The methane Cl spectrum of arenechromium and -molybdenum (54) show protonation at the metal giving a protonated parent or molecular ion. Risby et al. have studied the isobutane Cl mass spectra of lanthanide 2,2,6,6-tetramethylheptane-3,5-dionates[Ln(thd)3] (55) and 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-oetanedione [H(fod)] lanthanide complexes (56). These latter complexes have been suggested as a means of analysis for the lanthanide elements. 

In this latter reaction, the iridiabenzene complex cleanly displaces the para-xylene ligand so as to form complex 68, in which the iridiabenzene acts as if it were a normal pMigand coordinated to the molybdenum tricarbonyl moiety. 

The (/ -complexes all undergo thermal rearrangement to /2, /4-bicyclo[4.2.1]nona-2,4,7-triene tricarbonyl complexes. The possible mechanism of the rearrangement of the molybdenum complex has been thoroughly investigated by deuterium labeling and kinetic studies228. 

A number of readily reversible cr-7r rearrangements have been observed wherein a labile ligand such as carbon monoxide is lost by pyrolysis or photolysis, producing a coordinatively unsaturated metal center, which then regains coordinative saturation by means of a tr-n rearrangement. For example, irradiation of o--alkyl-7r-cyclopentadienyl-molybdenum tricarbonyl (15) produces the rr-allene complex (16) (25). These... 

While arsabenzene does not act as a nucleophile toward hard acids, it does form a-Mo(CO)5 complex 57 on treatment with pyridine-Mo(CO) and boron trifluoride etherate100). Qualitatively complex 57 seems rather weak since on heating it is destroyed, forming small quantities of tc-Mo(CO)3complex 58 101). This rt-complex is more conveniently prepared directly from arsabenzene and Mo(CO)6 or from acid-catalyzed displacement from tris-(pyridine)molybdenum tricarbonyl. 

Richard followed the course of the reactions of Cr(CO)6 and Mo(CO)6 with hexamethylborazine by UV-vis spectroscopy but although he observed that the intensity of the absorption maximum of the hexacarbonyls at around 290 nm decreased and a new band at around 350 nm appeared, he was unable to identify the new product. Experiments with other starting materials such as norborna-diene chromium and molybdenum tetracarbonyl or tris(aniline) molybdenum tricarbonyl which readily react with arenes by ligand exchange, also failed. The key to success was to use tris(acetonitrile) chromium tricarbonyl as the precursor, which in dioxan under reduced pressure afforded the desired hexamethylborazine chromium tricarbonyl as a stable crystalline solid in 90% yield. This was the breakthrough and, after we had communicated the synthesis and spectroscopic data of the complex in the January issue 1967 of Angewandte Chemie, Richard finished his work and defended his Ph.D. thesis in June 1967. Six months before, in December 1966,1 defended my Habilitation thesis in front of the faculty and became Privatdozent (lecturer) on the 1st of January 1967. 

Apart from the di- and oligoolefm iron tricarbonyl complexes, which nowadays are frequently used in organic synthesis [71, 72], the chemistry of the readily accessible cyclohepatriene chromium and molybdenum tricarbonyls 2 and 3 was the focus of intense research efforts as well. Only a few months after the synthesis of 2 and 3 was published [58,59], both Hyp Dauben and Peter Pauson reported that these compounds react with triphenylmethyl tetrafluoro-borate in methylene chloride to give the tropylium complexes 4 and 5 in excellent yield (Scheme 7.1) [73, 74]. Later this method of hydride abstraction was also used for the preparation of the tropylium cation itself and subsequently led to the generation of several cationic rc-complexes of iron, manganese and cobalt [71, 72], The reactions of the cations of 4 and 5 with nucleophilic... 

As indicated in Section 14.20.3.4, borepins can react with organometallics to form complexes in which the borepin ring serves as an rf ligand to the metal. Thus, 1-methylborepin 15 reacted with tris(pyridine)molybdenum tricarbonyl to afford the corresponding molybdenum complex 16 as a red, air-sensitive oil, as in Equation (1) <19970M1884>. 

A variety of transition metals, for example, chromium, molybdenum, tungsten, iron, vanadium, manganese, and rhodium can be used to prepare relatively stable j -arene complexes (see Arene Complexes). Reactions of j -arene chromium tricarbonyl complexes have been extensively examined, and numerous reviews are available. Although chromium complexes are by far the most utilized in organic synthesis, complexes of iron and manganese are emerging as potentially useful alternatives. 

The structure of cycloheptatriene-molybdenum tricarbonyl (XXX, M = Mo) was subsequently confirmed by x-ray analysis (76). The six olefinic carbon atoms were found to be approximately planar and symmetrically bonded to the metal, with the methylene carbon bent away from the latter. Carbon-carbon ring distances indicated alternate double and single bonds in the planar portion of the molecule, rather than a delocalized TT-electron system, as was originally suggested. The analogous complex (C7H8)W(C0)3 was subsequently described in the literature (62, 164). 

Although Able et al. (2, 8) had originally set out to prepare 7r-cyclo-heptatrienyl complexes of metals, the cycloheptatriene complexes they actually obtained served as key intermediates in forming the former complexes. In 1958 Dauben and Honnen (61) reported that cycloheptatriene-molybdenum tricarbonyl reacted with triphenylmethyl tetrafluoroborate in methylene chloride solution with abstraction of hydride ion from the molybdenum complex. The reaction products, obtained in nearly quantitative yields, were triphenylmethane and the 7r-cycloheptatrienyl complex [(7r-C7H7)Mo(CO)3]+BF4 . 

Hexakistrifluorophosphinechromium (and molybdenum) complexes are formed by treating the corresponding dibenzene metal derivative with PF3 at high pressure 153, 155). Different products are obtained from benzenetricarbonylchromium and PFg, depending on whether the reaction is carried out at elevated temperatures and pressures or with UV irradiation 54,155). Mesitylenemetal tricarbonyl complexes behave similarly. 

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