Six-membered cyclometallated derivatives of platinum(II) derived from 2-benzylpyridines. Crystal and molecular structure of [Pt(L)(Ph 3P)Cl] (HL = 2-(1-methylbenzyl)pyridine)

Abstract

The reaction of K 2[PtCl 4] with 2-(1-methylbenzyl)pyridine, HL, and 2-benzylpyridine, HL', affords the cyclometallated species [{Pt(L)Cl} 2] ( 1) and [{Pt(L')Cl} 2] ( 2), respectively. The chloride bridge in complex 1 can be split by neutral or anionic species to give the monomeric, [Pt(L)(Ph 3P)Cl], as two isomers, trans-P-Pt-C ( 3) and trans-P-Pt-N, ( 4), [Pt(L)(py)Cl] ( 5), [Pt(L)(CO)Cl] ( 6), [Pt(L)(CNCH 2SO 2C 6H 4CH 3-4)Cl] ( 7), [Pt(L)(acac)] (Hacac = 2,4-pentanedione) ( 8), [Pt(L)(dppm)][BF 4] (dppm = bis(diphenyl-phosphino)methane) ( 9), [Pt(L)(dppe)][BF 4] (dppe = bis(diphenylphosphino)ethane) ( 10) and [Pt(L)(dipy)][BF 4](dipy = 2,2'-dipyridine) ( 11). Similarly, compound 2, by reaction with Ph 3P, affords [Pt(L')(Ph 3P)Cl], as two isomers, trans-P-Pt-C ( 12) and trans-P-Pt-N ( 13). Reaction of compounds 1 or 4 with AgBF 4 in acetonitrile affords [Pt(L)(CH 3CN) 2 IBF 4] ( 14) or [Pt(L)(Ph 3P)-(CH 3CN)][BF 4] ( 15). From these, [Pt(L)(Ph 3P) 2][BF 4] ( 16), [Pt(L)(Ph 3P)(CO)][BF 4] ( 17) and [Pt(L)(Ph 3P)(py)][BF 4] ( 18), can be obtained by displacement of the coordinated acetonitrile. The new complexes were characterized by IR, 1H and 31P NMR and FAB-MS spectroscopic techniques. The NMR spectra at room temperature of most of the species derived from HL give evidence for the presence in solution of two diastereomers a and b. The structure of one diastereomer of complex 4 has been solved by single crystal X-ray diffraction, 4b. The platinum atom is in an almost square planar geometry with a P-Pt-N trans arrangement: Pt-N = 2.095(3), Pt-C = 1.998(4), Pt-P = 2.226(1) and Pt-Cl = 2.400(1) Å. The six-membered cyclometallated ring is in a boat conformation, with the CH 3 group in an equatorial position, i.e pointing away from the metal. Attempts to obtain [{Pt(L″)Cl} 2] (HL″ = 2-(dimethylbenzyl)pyridine), afforded an insoluble product heavily contaminated by platinum metal; treatment of this crude material with Ph 3P gave [Pt(L″)(Ph 3P)Cl] ( 19).