Contrasting Thermal and Photochemical Intramolecular Coupling in Alkynylphsphine Platinum (II)

Zusammenfassung

The thermal and photochemical transformations of a series of alkynylphosphine platinum(II) complexes are described. Compounds [Pt](PPh 2C≡CR) 2 ([Pt] = cis-Pt(C 6F 5) 2, R = Ph, Tol) rearrange thermally to generate naphthalene-based diphenylphosphine complexes (1a, 1b) containing the fragment {C 10H 5-1-Ph-2,3-κPP′(PPh 2) 2} or {7-CH 3-C 10H 4-1-Tol-2,3- κPP′(PPh 2) 2}, formed by intramolecular coupling of two adjacent PPh 2C≡CR ligands. By contrast, irradiation of these alkynylphosphine derivatives in toluene results in the formation of a mixture of 1a/1b and the 1,2-diphosphino-alk-1-ene complexes [Pt]{PPh 2C-(Ph)=C(R)PPh(C≡CR)} (R = Ph, 2a; Tol, 2b) in a final ratio of 60:40. However, irradiation of the mixed alkynylphosphine derivatives [Pt](PPh 2C≡CR)(PPh 2C≡Ct-Bu) gives selectively [Pt]{Ph 2PC(Ph)= C(R)PPh(C≡Ct-Bu)} (R = Ph, 3a; Tol, 3b; t-Bu, 3c) as result of a P-C(Ph) activation of a tert-butylalkynylphosphine, PPh 2C≡Ct-Bu. Under thermolysis, bis(tert-butyl)alkynyl derivatives produce no evidence of any cyclization product, but the mixed alkynylphosphine derivatives [Pt](PPh 2C≡CR)-(PPh 2C≡Ct-Bu) evolve giving small amounts of 1a/1b and trans-[Pt(C 6F 5) 2(PPh 2C≡Ct-Bu) 2], 4. Under photolytic conditions, the diynyl phosphine derivatives [Pt](PPh 2Ca≡CC 6H 4C≡CR) 2 (R = Ph, t-Bu) rearrange directly to the naphthalene complexes [Pt]{7-C≡CR-C 10H 4-1-(C 6H 4-pC≡CR)-2,3- κPP′(PPh 2) 2} (R = Ph, 5a; t-Bu, 5c), resulting from the intramolecular coupling of the two inner alkynyl fragments, with no observable intermediates. Finally, site-selective activation takes place by photochemical or thermal treatment of [Pt](PPh 2C≡CPh)(PPh 2H), 6. Thus, while under photochemical conditions complex 6 yields selectively [Pt]{Ph 2PC(Ph)=C(Ph)PPhH}, 7, by a ligand rearrangement coupling process involving activation of a P-C(Ph) bond, the regioisomer [Pt]{Ph 2PC(H)=C(Ph)PPh 2}, 8, is generated by a thermal activation of the P-H bond. © 2006 American Chemical Society.