Cationic linear triphos, L[PhP(CH2CH2PPh2)(2)], alkyne complexes of molybdenum(II) and tungsten(II); crystal structures of [WI(CO)-(L-P,P ',P '')(eta(2)-MeC2Me)](2)[W6O19], [WI(CO)(L-P,P ',P '')(eta(2)-MeC2Me)][BPh4] and [MoBr2(O){Ph2P(CH2)(2)PPh(CH2)(2)POPh2-P,P ',O}]

Equimolar quantities of [MoX(Y)(CO)(NCMe)(eta(2)-RC2R)(2)] and L [= PhP(CH2 CH2PPh2)(2)] reacted in CH2Cl2 at room temperature to give the cationic tri dentate linear triphos complexes [MoX(CO)(L-P,P',P ")(eta(2)-RC2R)]Y 1-5 (X = Y = Pr, R = Me or Ph; X = Cl, Y = I, R = Me or Ph; X = Pr, Y = I, R = Me ) in high yield. Refluxing the tungsten complexes [WX2(CO)(L-P,P')(eta(2)-R C2R')] in dry acetonitrile afforded the cationic complexes, [WX(CO)(L-P,P', P ")(eta(2)-RC2R')]X 6-8 (X = Pr or I, R = R' = Me; X = 1, R = Me, R' = Ph) , whereas refluxing [WI2(CO)(L-P,P ")(eta(2)-MeC2Me)] in slightly wet aceto nitrile yielded the unusual crystallographically characterised complex [WI( CO)(L-P,P',P ")(eta(2)-MeC2Me)](2)[W6O19] 9. Silver tetrafluoroborate react ed with an equimolar amount of [MI2(CO)(L-P,P')(eta(2)-RC2R')] in acetonitr ile to give the cationic complexes [MI(CO)(L-P,P',P ")(eta(2)-RC2R')][BF4] 10-13 (M = Mo, R = R' = Me or Ph; M = W, R = R' = Me, R = Me, R' = Ph). The tetraphenylborate complexes [WI(CO)(L . P,P',P ")(eta(2)-RC2R')][BPh4] (R = R' = Me 14, R = Me, R' = Ph 15) were prepared by an iodide exchange react ion of [WI(CO)(L-P,P',P ")(eta(2)-RC2R')]I with Na[BPh4] in acetonitrile. T he crystal structure for 14 has been determined. The dicationic complexes [ W(CO)(NCMe)(L-P,P',P ")(eta(2)-RC2R')][BF4](2) 16-18 (R = R' = Me or Ph; R = Me, R' = Ph) were prepared by treating [WI2(CO)(L-P,P')(eta(2)-RC2R')] wi th 2 equivalents of Ag[BF4] in acetonitrile. The cationic bromomolybdenum c omplexes [MoBr(CO)(L-P,P',P ")(eta(2)-RC2R)]Br (R = Me or Ph) rearrange in refluxing CHCl3 in air to give the unusual molybdenum(IV) product [MoBr2(O) {Ph2P(CH2)(2)PPh(CH2)(2)POPh2-P,P',O}] 19, which has been crystallographica lly characterised.