Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 86. Aikylidyne(carbaborane)molybdenum–gold, –rhodium and –iron complexes; crystal structure of [NEt4][MoFe2(µ3-CC6H4Me-4)(µ-σ : σ′ : η5C2B9H7Me2)(CO)8]

Abstract

The alkylidyne–molybdenum complex [NEt₄][Mo(CC₆H₄Me-4)(CO){P(OMe)₃}(η⁵-C₂B₉H₉Me₂)] has been prepared, and used to prepare compounds with bonds between molybdenum and gold, rhodium, and iron. Reactions of the molybdenum compound with [AuCl(PPh₃)],[Rh(cod)(PPh₃)₂][PF₆](cod = cyclo-octa-1,5-diene), and [Fe₂(CO)₉] afford, respectively, the complexes [MoAu(µ-CC₆H₄Me-4)(CO){P(OMe)₃}(PPh₃)(η⁵-C₂B₉H₉Me₂)], [MoRh(µ-CC₆H₄Me-4)(µ-CO){P(OMe)₃}(PPh₃)₂(η⁵-C₂B₉H₉Me₂)], and [NEt₄][MoFe₂(µ₃-CC₆H₄Me-4)(µ-σ : σ′ : η⁵-C₂B₉H₇Me₂)(CO)₈]. The structure of the latter has been established by X-ray diffraction. There are two crystallographically independent anions with their associated cations in the asymmetric unit but with overall very similar geometries. In the anions a triangle of metal atoms is symmetrically capped on one side by the alkylidyne ligand. On the other side of the triangle the molybdenum atom is η⁵-ligated by the C₂B₉cage, but two boron atoms in the pentagonal face are σ bonded to the two iron atoms. The molybdenum carries two carbonyl groups and each of the iron atoms is bonded by three of these ligands. The reaction between [Fe₂(CO)₉] and [NEt₄][Mo(CC₆H₄Me-4)(CO){P(OMe)₃}(η⁵-C₂B₉H₉Me₂)] also affords the novel mononuclear molybdenum compound [NEt₄][Mo{σ,η⁵-CH (C₆H₄Me-4)C₂B₉H₈Me₂}(CO)₃]. Protonation (HBF₄·Et₂O) of CO-saturated CH₂Cl₂solutions of the latter gives the neutral complex [Mo(CO)₄{η⁵-C₂B₉H₈(CH₂C₆H₄Me-4)Me₂}]. Protonation in the presence of an excess of PMe₃ gives a mixture of the two compounds [Mo(CO)₃(L){η⁵-C₂B₉H₈(CH₂C₆H₄Me-4)Me₂}](L = PMe₃ or CO). The n.m.r. data (¹H, ¹³C-{¹H},¹¹B-{¹H}, and ³¹P-(¹H}) for the new compounds are reported and discussed.