Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 77. Reactions of iron–molybdenum compounds with alkynes; crystal structures of [MoFe{µ-C(C6H4Me-4)C(CHMe)CH2C(Me)C(Me)}(CO)4(η-C5H5)], [MoFe{µ-C(C6H4Me-4)C(CHMe)CH2}(CO)5(η-C5H5)], and [MoFe{µ-C(C6H4Me-4)C(CH2PMe3)CHMe}(CO)5(η-C5H5)]

Abstract

The compounds [MoFe(µ-CR)(CO)₆(η-C₅H₅)](1a) and [MoFe₂(µ₃-CR)(µ-CO)(CO)₈(η-C₅H₅)](2a)(R = C₆H₄Me-4) react with PhCCPh to give the same molybdenum–iron complex [MoFe{µ-C(R)C(Ph)C(Ph)}(CO)₅(η-C₅H₅)](3a). In contrast, MeCCMe reacts with (2a) to yield [MoFe{µ-C(R)C(CHMe)CH₂C(Me)C(Me)}(CO)₄(η-C₅H₅)](4), and with (1a) to yield [MoFe{µ-C(R)C(CHMe)CH₂}(CO)₅(η-C₅H₅)][two isomers, (5a) and (5b)]. The molecular structures of (4) and (5a) have been established by X-ray diffraction. In (4) the Mo–Fe bond [2.784(1)Å] is bridged by the branched six-carbon atom chain of the C(R)C(CHMe)CH₂C(Me)C(Me) ligand, with the C(R)C(CHMe) fragment η³ co-ordinated to the molybdenum atom. This metal centre is also σ bonded to the terminal CMe group, and co-ordinated by one carbonyl and an η-C₅H₅ ligand. Both CMe groups are bonded to the iron centre, as is also the CR fragment and three terminal carbonyls. In (5a) the Mo–Fe separation (4.027 Å) is non-bonding, the two metal atoms being linked via a C(R)C(CHMe)CH₂ unit. The molybdenum atom is η³ co-ordinated by the CC₆H₄Me-4 group, while the Fe(CO)₃ fragment is η⁴ co-ordinated by four carbon atoms of the substituted trimethylenemethane moiety (η-C₅H₅)(OC)₂MoC(R)C(CHMe)CH₂. In (5a) the Mo(CO)₂(η-C₅H₅) and CH₂ groups are cisoid, whereas in (5b) they are transoid. Treatment of the isomers (5) with PMe₃ yields two zwitterionic complexes [MoFe{µ-C(R)C[C(H)Me(PMe₃)]CH₂}(CO)₅(η-C₅H₅)](6a) and [MoFe{µ-C(R)C(CH₂PMe₃)CHMe}(CO)₅(η-C₅H₅)](6b), of which the latter isomer is the more stable, allowing an X-ray diffraction study to be made. In (6b) a long Mo–Fe [2.831(2)Å] single bond is spanned by the C(R)C(CH₂PMe₃)CHMe group, with the Mo(CO)₂(η-C₅H₅) fragment attached to CR[2.20(1)Å] and with the Fe(CO)₃ moiety η³ co-ordinated by the three atoms C(R)C(CH₂PMe₃)CHMe. With CO, compound (5) yields [MoFe{µ-C(O)C(R)C(CHMe)CH₂}(CO)₆(η-C₅H₅)] formed as a 1 : 1 mixture of two isomers, (7a) and (7b). In these isomers an Fe(CO)₃ group is ligated by a substituted trimethylenemethane, the central carbon of which carries CH₂, CHMe, and C(R)C(O)Mo(CO)₃(η-C₅H₅) groups as substituents; there being no molybdenum–iron bond. Isomers arise according to whether the CH₂ and CHMe groups are cisoid or transoid to those of R or C(O)Mo(CO)₃(η-C₅H₅). Treatment of the dimetal compound [MoFe(µ-CR)(CO)₅(PMe₃)(η-C₅H₅)] with MeCCMe affords the complex [MoFe{µ-C(R)C(CHMe)CH₂C(O)}(µ-CO)(CO)₃(PMe₃)(η-C₅H₅)]. The n.m.r. (¹H and ¹³C-{¹H}) data for the new compounds are reported and discussed in terms of the structures.