Synthesis and reactions of η-cycloheptatrienyl derivatives of molybdenum

Abstract

An improved route to [Mo(η-C₇H₇)(η-C₇H₉)]2 has been found which involves the reduction of MoCl₅ with sodium amalgam in the presence of cycloheptatriene followed by thermolysis. Compound 2 can be oxidised with a half equivalent of iodine or tetrafluoroboric acid forming the corresponding cation [Mo(η-C₇H₇)(η-C₇H₉)]⁺3, which reacts with ethanol or an excess of iodine to yield the binuclear cations [(η-C₇H₇)Mo(µ-X)₃Mo(η-C₇H₇⁺](X = OEt 4 or I 5 respectively). Treatment of 2 with 1 equivalent of iodine, bromine or an excess of PhlCl₂ in the presence of a weak co-ordinating solvent or σ-donor affords the 17-electron compounds [Mo(η-C₇H₇)LX₂][L = tetrahydrofuran (thf), MeCN, PPh₃, PMe₃ or Et₂S; X = Cl, Br or I). Treatment of [Mo(η-C₇H₇)(MeCN)I₂]11 with [NBu₄]I gives [NBu₄][Mo(η-C₇H₇)I₃]18 and reduction of 11 with sodium amalgam in the presence of 1,2-bis(dimethylphosphino)ethane (dmpe), 1,2-bis(diphenylphosphino)ethane (dppe) or PMe₃ gives [Mo(η-C₇H₇)(dmpe)I]19, [Mo(η-C₇H₇)(dppe)I]20 or [Mo(η-C₇H₇)(PMe₃)₂I]13, respectively. Compound 11 also reacts with Na(C₅H₄R)(R = H or Me) or lithium indenide to yield the mixed-sandwich compounds [Mo(η-C₇H₇)(η-C₅H₄R)](R = H 21 or Me 22) or [Mo(η-C₇H₇)(η-C₉H₇)]23. The crystal structures of [NBu₄][Mo(η-C₇H₇)I₃]18 and [Mo(η-C₇H₇)(η-C₅H₄Me)]22 have been determined. Compound 22 reacts with 1 equivalent of tetracyanoethene (tcne) to give the electron-transfer complex [Mo(η-C₇H₇)(η-C₅H₄Me)][tcne]24 while compound 21 reacts with 1 equivalent of 7,7,8,8-tetracyanoquinodimethane (tcnq) to yield [Mo(η-C₇H₇)(η-C₅H₅)]₂[tcnq]25.