Molybdenum complexes with isocyanides

Seven and eight coordinate molybdenum complexes and related molybaenum(IV) oxo complexes with cyanide and isocyanide ligands. S. J. Lippard, Prog. Inorg. Chem., 1976, 21, 91-103 (44). 

A number of attempts have been made over the years to develop reproducible synthetic routes to six- and seven-coordinate isocyanide complexes of molybdenum and tungsten. Two of the older methods, namely, the reaction of the hexacarbonyls with halogens in the presence of an isocyanide (775,116) or reactions of the salt Ag4Mo(CN)8 with isocyanides (74), have given six- and seven-coordinate products. Recently, however, the discovery of the reductive or nonreductive cleavage of multiple metal - metal bonds in dinuclear group VIA compounds by isocyanides has provided a facile route to the synthesis of a variety of homoleptic and related isocyanide complexes of these metals in reasonable yields. 

Cycloheptatrienes with chromium, 5, 337 in molybdenum carbonyls, 5, 480 tj7-Cycloheptatrienyl complexes, with tungsten carbonyls and isocyanides, 5, 693 Cycloheptatrienyl compounds actinide complexes, 4, 227 with actinides, 4, 226 lanthanide complexes, 4, 122... 

Lippard, Stephen J., Seven and Eight Coordinate Molybdenum Complexes and Related Molybdenum (IV) Oxo Complexes, with Cyanide and Isocyanide... 

Cyanides.—A concise review of the seven- and eight-co-ordinate molybdenum complexes and related molybdenum(vi) 0x0 complexes, with cyanide and isocyanide ligands has appeared and Group Via cyanide complexes have been reviewed within the broader scope of transition metal cyanides. ... 

Molybdenum(IV) and tungsten(IV) compounds may be obtained by alkylation utilizing RX, while reactions of [M(CN)g] with isocyanides RNC lead to complexes in lower oxidation state. 

A more complex reaction is involved in the cooligomerization of acetylenes and tert-butyl isocyanide using nickel acetate as the catalyst (Scheme 20)43 the nature of intermediate complexes leading to the formation of 2-cyano-5-terf-butylaminopyrroles has not been established. Cocyclization of tert-butyl isocyanide with coordinated hexafluoro-2-butyne gives rise to coordinated cyclopentadienone anils for molybdenum systems,44 hence the nature of acetylene substitutents and of the organometallic catalyst play crucial roles in these processes. The pyrrole products from the former reaction can be decomposed by sulfuric acid and the overall sequence provides a simple synthesis of 5-amino-2-cyanopyrroles (Scheme 20). 

In a three-component reaction, a cationic platinum isocyanide complex [(Ph3P)2Pt(CNR)Cl][BF4] is reacted with a /3-bromoamine and butyl lithium to give an imidazoldin-2-ylidene complex.This transformation can be a two-component reaction if the isocyanide ligand contains already the necessary amine functionality. This was shown for chromium, molybdenum, tungsten, and rhenium carbonyls. 

Molybdenum carbonyl-isocyanide complexes may be obtained as in Section 36.2.2.1.1. In most respects isocyanides behave in a very similar way to carbon monoxide, with which they are isoelectronic. As for the carbonyls, the isocyanide complexes may be regarded as derivatives of [Mo(CNR)6] and have been reviewed comprehensively.la,b... 

Isocyanides are rather more reactive than CO at low-valent molybdenum centres and may react with nucleophiles, e.g. R NH2, to give carbene complexes,la e.g. equation (2), or with electrophiles to give carbyne complexes,1,4 e.g. (3). 

A number of isocyanide complexes, [Mo(CN)4(CNR)4] (R = Me, Pr, Bu allyl, NCPh2), have been made by the action of RI on Ag4[Mo(CN)8]. The crystal structure of [Mo(CN)4(CNMe)4] shows a dodecahedral geometry, with the CN- ligands at 2.177(8) A and the MeNC ligands at 2.148(8) A from the molybdenum.207 Both 13C NMR and vibrational spectroscopy indicate that only one isomer is present in solution. 

The striking advance since 1973 has been the synthesis of homoleptic isocyanides for vanadium and almost all of the post-group-VIA metals up to group IB (see Table I), and this has been helped in some respects by synthetic rationale. For example, the discovery of the simple reductive or nonreduc-tive cleavage of multiple metal-metal bonds in suitable dinuclear complexes of molybdenum and tungsten has provided a high yield route to W(CNPh)6 and [M(CNR)7]2+ (M = Mo, W) and related complexes (5-14). During these studies the series [M(CNR)7]2+ was completed with the isola-... 

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