AN UNUSUAL TRIMERIZATION REACTION OF AN ALKYNE ON IRIDIUM

Reactions between mer-(Me3P)3Ir(H)(H)(Cl) and 2-ethynylpyridine in wat er or mer-(Me3P)3Ir(H)(Ph)(Cl) and 2-ethynylpyridine and Tl[PF6] in CH 2Cl2 both lead to the formation of an unusual 3.3.0-azairidabicyclooct atriene, 3. Complex 3 was characterized by single crystal X-ray diffra ction and was found to crystallize in the triclinic space group P1BAR with a = 12.060(3) angstrom, b = 12.512(3) angstrom, c = 14.833(3) ang strom, alpha = 87.25(2)degrees, beta = 73.21(2), gamma = 69.93(2)degre es and V = 2009.4(9) angstrom3 for Z = 2. Complex 3 appears to form vi a a [GRAPHICS] 3, P = PMe; py = pyridyl sequence of reactions involvin g (i) coupling of two equivalents of 2-ethynylpyridine at iridium (I) to yield a metallacylopentadiene complex; (ii) addition of a third equ ivalent of 2-ethynylpyridine; (iii) rearrangement of the third equival ent of 2-ethynylpyridine to a vinylidene; and (iv) nucleophilic attack of a pendant pyridine on the a carbon of the vinylidene.