Appreciably bent sp carbon chains:: synthesis, structure, and protonation of organometallic 1,3,5-triynes and 1,3,5,7-tetraynes of the formula (η5-C5Me5)Re(NO)(PPh3)((CC)n-p-C6H4Me)

The diyne (eta(5)-C5Me5)Re(NO) (PPh3)(C=CC-CSiMe3) is elaborated to (eta(5)-C5Me5)Re(NO)(PPh3)(C=CC=CC=CSiR3)(R = Me, 3a; Et, 3b) by sequences involving n-Bu4N+F- in aqueous THF to give (eta 5-C5Me5)Re(NO)(PPh3)(C=CC=CH) (91%), n-BuLi/ CuI or t-BuOCu to give (eta(5)-C5Me5)Re(NO)(PPh3)(C=CC=CCu) (4), and coupling with IC=CSiMe3 (48%) or BrC=CSiEt3 (84-65%). Complex 3b is similarly converted to (eta(5)-C5Me5)Re(No)(PPh3)(C=CC=CC=CH) (88%) and (eta(5)-C5Me5)Re(No)(PPh3(C=CC=CC=CCu) (6). Reactions of 4 and 6 with BrC=C-p-C6H4Me give the title compounds (eta(5)-C5Me5)Re(NO)(PPh3)((C=C)(n)-p-C6H4Me) (n = 3, 7; 4,8; 77-66%). Optimized one flask conversions of 1a and 3b to 7 (81%) and 8 (71%) are described. The crystal structures of 7 (monoclinic, P2(1)/c, a/b/c = 17.951(8)/8.377(5)/22.160(9) Angstrom, beta = 103.63(5)degrees, Z = 4), and 8 (monoclinic, P2(1)/n, a/b/c = 8.426(3)/16.400(6)/25.400(9) Angstrom, beta = 97.51(3)degrees, Z = 4) show markedly curved sp carbon chains-much more than hexatriynes or octatetraynes reported to date. The bond angles associated with the Re(C=C)(n)C moieties (min/max/avg) are 169.1(10)degrees/178.8(13)degrees/174.7 degrees (7) and 170.0(9)degrees/178.8(10)degrees/175.7 degrees (8). Other structural features are normal, and bending is provisionally ascribed to packing forces. Reaction of 7 and HBF4. OEt2 gives the cationic vinylidene complex [(eta(5)-C5Me5) Re(NO)(PPh3) (C=C(H)C=CC=C-p-C6H4Me)](+) BF4-, the structure of which is established by extensive NMR analyses. (C) 1999 Elsevier Science S.A. All rights reserved.