Cis- and trans-bis(diphenylphosphino)ethene seven-coordinate complexes of molybdenum(II) and tungsten(II). Crystal structures of [MI2(CO)3(cis-dppen)] {M=Mo or W; dppen=bis(diphenylphosphino)ethene}, [WI(CO)2(cis-dppen)2]I, [MI2(CO)2{P(OR)3}(cis-dppen)] (

Equimolar quantities of [MI2(CO)3(NCMe)2] (M=Mo or W) and cis-dppen {dppen=Ph2PCHCHPPh2} react in CH2Cl2 at room temperature to give good yields of the crystallographically characterised complexes [MI2(CO)3(cis-dppen)] (1 and 2). Treatment of [WI2(CO)3(NCMe)2] with two equivalents of cis-dppen affords the crystallographically characterised cationic complex [WI(CO)2(cis-dppen)2]I (3). Reaction of [MI2(CO)3(NCMe)2] with one equivalent of cis-dppen, followed by addition of an equimolar amount of P(OR)3 affords the mixed ligand complexes [MI2(CO)2{P(OR)3}(cis-dppen)] (M=Mo or W; R=Me, Et, iPr, nBu or Ph) (4–13). The X-ray crystal structures for M=Mo, R=Me; M=W, R=Et or Ph are also determined. Treatment of equimolar quantities of [MoI2(CO)3(NCMe)2] and P(OiPr)3 gave [MoI2(CO)3(NCMe){P(OiPr)3}], which reacted in situ with half an equivalent of trans-dppen to furnish the bimetallic phosphine-bridged complex [{MoI2(CO)3{P(OiPr)3}}2(μ-trans-dppen)] (14).