SYNTHESIS OF THE COMPLEXES [N(PPH3)2][M(CO)2(ETA-3-C3H5)-(ETA-6-7,9-C2B10H10ME2)](M=MO OR W) - CRYSTAL-STRUCTURE OF [N(PPH3)2][WBR(CO)3(ETA-6-7,9-C2B10H10ME2)]

Treatment of the compounds [MBr(CO)2(NCMe)2(eta3-C3H5)] (M = Mo or W) with Na2[7,9-C2B10H10Me2] in tetrahydrofuran, followed by addition of [N(PPh3)2]Cl, affords the salts [N(PPh3)2)(M(CO)2(eta6-C3H5)(eta6-7 9-C2B10H10Me2)]. Reactions of [N(PPhl)2]2[M(CO)3(eta6-7,9-C2B10H10Me2)] with an excess of allyl bromide generate the complexes [N(PPh3)2IMBr(CO)3(eta6-7,9-C2B10H10Me2)] via an allyl-coupling process. The structure of the latter (M = W) has been determined by X-ray diffraction. The preparation of the molybdenum salt [N(PPh3)2][MoBr(CO)3(eta6-7,9-C2B10H10Me2)] by this route was accompanied by the formation of small amounts of the complex [N(PPh3)2][MoBr(CO)3(eta5-7,9-C2B9H9Me2)] resulting from ejection of a BH vertex from the cage. Indeed, it was observed that in CH 2Cl2 solutions, the former species was slowly converted into the latter at ambient temperatures. Protonation (aqueous HBr) of the salts [N(PPh3)2][M(CO)2(eta-C3H5)(eta6-7 6-7,9-C2B10H10Me2)] in the presence of an atmosphere of CO also yields the compounds [N(PPh3),][MBr(CO),(eta6-7,9-C2B10H10Me2)], but if the molybdenum compound is protonated in the absence of CO the complex [N(PPhl)2][MoBr(CO),(eta5-7,9-C2B9H9Me2)] is formed directly. The NMR data for the new compounds are reported and discussed, as are the possible pathways of their formation.