摘要:
                                The labile W(0) source [W(CO)3(NCC2H5)3] (2) reacts with the bulky alkyne bis(trimethylsilyl)acetylene (BTMSA) under reduced pressure to give the tris(alkyne) complex [W(Me3SiC = CSiMe3)3(CO)] (3), which has a low barrier to alkyne rotation.  The terminal alkyne PhC = CH reacts similarly with 2 to give the tris(alkyne) complex [W(PhC = CH)3(CO)] (4), isolated as an oil and derivatized by substitution with PPh3 to give [W(PhC = CH)3(PPh3)] (6).  Complex 6 is monoisomeric, with all three alkynes oriented with the acetylenic hydrogens proximal to the phosphine, while 4 exists as a mixture of isomers.  C-13 NMR spectroscopy indicates that 4 exists in C6D5CD3 as a mixture of 4(3) (4%), 4(2) (64%), and 4(1) (32%), with three, two, and one acetylenic hydrogen, respectively, proximal to the carbonyl.  Phosphine substitution is also feasible with the more sterically crowded tris(alkyne) substrate [W(PhC = CPh)3(CO)] (7), which reacts with PMe2Ph to give [W(PhC = CPh)3(PMe2Ph)] (8), in which DELTA-G-double-dagger for alkyne rotation is 13.2 (3) kcal mol-1.  The importance of steric factors in determining bonding interactions and alkyne rotation barriers in [W(RC = CR)3(L)] complexes was evaluated by comparison of the NMR characteristics of [W(PhC = CPh)3(SnPh3)]- (9-) with those of [W(PhC = CPh)3(SnMe3)]- (10-), prepared by naphthalenide reduction of 7 and addition of Me3SnCl.  The alkyne rotation barrier in 10- (DELTA-G-double-dagger = 12.7 (2) kcal mol-1) is similar to that in 9- (DELTA-G-double-dagger = 13.1 kcal mol-1), implying that steric factors are not dominant.  NMR parameters involving Sn-119 suggest that 9- and 10- are best thought of as complexes of ''[W(PhC = CPh)3]'' with R3Sn-anions.