Reactions of metallabromoalkanes [M{(CH2)nBr}(CO)3(η-C5H5)](M = Mo or W, n= 3 or 4) with transition metal anions. Dimetalla-alkane and cyclic carbene complex formation. Crystal and molecular structures of [(η-C5H5)(OC)3Mo{(CH2)4}Mo(CO)3(η-C5H5)] and [(η-C5H5)(OC)3MoW(CO)2{C–O–(CH2)2CH2}(η-C5H5)]