The reaction of cis-Me2Os(CO)4 with HBF4·Et2O affords the complex cis- (OC)4Os(FBF3)CH3 (2). The coordinated tetrafluoroborate of 2 is easily substituted by H2O, [Re(CO)5]-, [Re(CO)4(CN)CH3]- (from Re(CO)5CH3 and NaN(SiMe3)2), SCN- and PPhMe2 to give neutral or cationic complexes 4-6, 8, 9, respectively. The structure of cis-H3C(OC)4Os- Re(CO)5 has been determined by X-ray diffraction.

Organometallic Lewis Acids, LIVtOl. -M O ( C O )~( P P~~)~( O~S C F~)~: A New Precursor for an Organometallic Dicationic Lewis Acid with Three Accessible Coordination Sites The reaction of Mo(COj2(PPh3j2Br, (1) with Ag03SCF3 gives 1-propyne leads to the monoalkyne complexes Mo(C0)the bis(trif1ate) complex M o ( C O )~( P P~~)~( O~S C F~)~ (3) which (MeC=CR)(PPh3)2(03SCF3)2 (9: R = Me; 10: R = Ph) in mocan be considered as a precursor for the 12-e-system "Mo-derate yield. In contrast, the bisalkyne complexes [M(CO)-(C0)2(PPh3)$+". According to the spectroscopic data one of (MeC=CMe),(PPh3)2(03SCF3)][CF3S03] (1 1: M = Mo; 12: the two coordinated CF3SO; anions is acting as a chelate M = W) are formed in high yield when a CH2C12 solution of ligand. Treatment of 3 and of the in situ generated W(CO)2-2-butyne is added to 1 and 2 in the presence of Ag03SCF3. (PPh3)2(03SCF3)2 (4) with H 2 0 affords the dinuclear hydroxo-At room temperature, 11 and 12 are highly fluxional in solubridged complexes [M2(p-OH)3(CO),(PPh3)4][CF3S03] (5: tion, while 9 and 10 are stereochemically rigid. Treatment of M = Mo; 6: M = W). Acetonitrile replaces the CF3S0y li-11 with acetonitrile yields [Mo(CO)(MeC=CMe),(PPh,),gands in 3 and 4 to afford the cationic complexes (NCMe)][CF3S03]2 (13). Compounds 3-13 (except 4) are [M(CO)2(PPh3)2(NCMe)3][CF3S03]2 (7: M = Mo; 8: M = W). characterized by IR, 'H-, 13C-, 19F-, and 31P-NMR spectros-The reaction of 3 with an excess of 2-butyne and 1-phenyl-copy.