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Contrasting thermal and photochemical intramolecular coupling in alkynylphosphine platinum(II) complexes
Garcia, Ana,Gomez, Julio,Lalinde, Elena,Moreno, M. Teresa
, p. 3926 - 3934 (2008/10/09)
The thermal and photochemical transformations of a series of alkynylphosphine platinum(II) complexes are described. Compounds [Pt](PPh 2C≡CR)2 ([Pt] = cis-Pt(C6F 5)2, R = Ph, Tol) rearrange thermally to generate naphthalene-based diphenylphosphine complexes (1a, 1b) containing the fragment {C10H5-1-Ph-2,3-κPP′(PPh2) 2} or {7-CH3-C10H4-1-Tol-2,3- κPP′(PPh2)2}, formed by intramolecular coupling of two adjacent PPh2C≡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]{PPh2C-(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](PPh2C≡CR)(PPh2C≡Ct-Bu) gives selectively [Pt]{Ph2PC(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](PPh2C≡CR)-(PPh2C≡Ct-Bu) evolve giving small amounts of 1a/1b and trans-[Pt(C6F 5)2(PPh2C≡Ct-Bu)2], 4. Under photolytic conditions, the diynyl phosphine derivatives [Pt](PPh 2Ca≡CC6H4C≡CR)2 (R = Ph, t-Bu) rearrange directly to the naphthalene complexes [Pt]{7-C≡CR-C 10H4-1-(C6H4-pC≡CR)-2,3- κPP′(PPh2)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](PPh2C≡CPh)(PPh 2H), 6. Thus, while under photochemical conditions complex 6 yields selectively [Pt]{Ph2PC(Ph)=C(Ph)PPhH}, 7, by a ligand rearrangement coupling process involving activation of a P-C(Ph) bond, the regioisomer [Pt]{Ph2PC(H)=C(Ph)PPh2}, 8, is generated by a thermal activation of the P-H bond.
