Alkylidyne-metal complexes structures

Up to March 2006 the molecular structures of about 40 alkylidyne complexes ligated by poly(pyrazolyl)borates had been reported, and structural data for the crystallographically characterised alkylidyne-metal complexes are compiled in Table II. Of these, Tp- and Tp -ligated complexes represent more than 80%, with one third of the total known structures being bi- and polymetallic complexes. Structural features of alkylidyne complexes in general have been discussed elsewhere and, accordingly, an attempt to restrict this discussion to features which are unique or characteristic of the scorpionate alkylidyne complexes has been made. 

Byers, P.K, Carr, N. and Stone, F.G.A. (1990) Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 106. Synthesis and reactions of the alkylidyne complexes [M ( CR)(CO)2 (C6F5)AuC(pz)3 j (M = W or Mo, R — alkyl or aryl, pz — pyrazol-l-yl) crystal structure of pjC PtAu(C6F5)( l3-CMe)(CO)2(PMe2Ph)2 (C6F5)AuC(pz)3 ]. Journal of the Chemical Society, Dalton Transactions, (12), 3701—3708. 

Scheme 1. Alkene-and alkyne-metal complexes may be formulated with metallacyclo-propane (A) or -propene (B) structures, respectively. Similarly, complexation of a metal atom with an alkylidene or alkylidyne group gives rise to a dimetallacyclopropane (C) or -propene (D) ring system.

H NMR shows that the alkyne ligand in 242 (R = H) rotates about the metal-alkyne bond axis with an activation barrier of only 50 kJ/mol. The structure of the diphenylacetylene complex 242 was determined by X-ray crystallography. The reaction shown in Eq. (183) was expected to generate alkylidyne alkyne complexes such as W(CPh)CI(PhC2R)(CO)-(PMe3)2. Such species are probably intermediates in the reaction however, a n conflict between the adjacent C=C and M=C triple bond systems... 

Early -block metal complexes containing one or two Qt-hydrogen atoms (see 24.47) may undergo a-hydrogen abstraction to yield carbene (alkylidene, 24.49) or carbyne alkylidyne, 24.50) complexes. The solid state structure of the product of reaction 24.45 confirms differences in the Ta—C bond lengths 225 pm for Ta—Caikyi and 205 pm for Ta Ccarbene-... 

The above summary of recent results indicates the remarkable scope, within the as-yet-undiscovered chemistry of the reagents 1 and 2, for the formation of unusual structures and the observation of new chemical processes. The future potential of these molecules stems from the union of alkylidyne-metal and metallacarbaborane complexes which they represent, and appears to offer unlimited opportunity for exploration. 

Further developments are likely as the chemistry of the compounds described above is explored. Moreover, entirely new dimensions may be added. For example, the synthesis of tungsten-alkylidyne complexes with carba-borane ligands with cage structures smaller than the icosahedral C2B9 fragment should result in the isolation of new electronically unsaturated metal cluster and electron-deficient molecules of types as yet unknown. 

Of the large number of /u.3-alkylidyne clusters known, only the title complexes have had their photochemical properties reported (194). The structure of CH3CCo3(CO)9 (163) consists of a triangle of metal-metal... 

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