102261-65-4Relevant academic research and scientific papers
Ring expansion of platinacyclobutanes: The scope and mechanism of the reaction
Burton, J. Thomas,Puddephatt, Richard J.
, p. 1312 - 1319 (2008/10/08)
New platinacyclobutylcarbinyl esters of formula Cl2L2PtCH2CR1(CHR2OR 3)CH2] (R1 = H, Me, or Ph; R2 = H or Me; R3 = methanesulfonyl or 4-nitrobenzoyl; L = pyridine or L2 = 2,2′-bipyridine) have been prepared and characterized. On solvolysis in aqueous acetone these complexes give the ring-expanded platinacyclopentanol products [Cl2L2PtCHR2CR1(OH)CH 2CH2], which have been isolated and characterized. The ring expansions occur with greater selectivity than in the corresponding solvolyses of cyclobutylcarbinyl esters, but the scope of the reactions is limited by the low thermal stability of the platinacyclobutane precursors. It was not possible to catalyze the ring expansion of platinacyclobutylcarbinols to the corresponding platinacyclopentanols. The solvolyses of [Cl2py2PtCH2CH(CH2OMs)CH 2] (3a, OMs = mesylate), [Cl2(bpy)PtCH2CH(CH2OMs)CH2] (3b), and [Cl2py2PtCH2CMe(CH2OMs)CH 2] (3c) in acetone-water (60% v/v) at 36°C follow good first-order kinetics and give the products [Cl2L2PtC1H2C2R(OH)C 3H2C4H2]. The solvolysis of 3a is retarded by the presence of free pyridine, and the limiting rate in the presence of excess pyridine is almost the same as for 3b. The solvolysis of 3c is affected only slightly by the presence of free pyridine. Solvolysis of analogous complexes labeled at the CH2O center with 13C (3a* and 3b*) or 2H (3a**, 3b**, 3c**) gave the products with the label at C1 or C3. In the absence of pyridine, 3a** and 3c** gave the corresponding products labeled at C1, 86% and 10%, respectively, and at C3, 14% and 90%, respectively, while in the presence of pyridine they gave the label at C1, 32% and 0%, and at C3, 68% and 100%, respectively. Complex 3b** gave the label at C1, 27%, and C3, 73%, as determined by integration of 2H{1H} NMR spectra. The data are rationalized in terms of a mechanism in which skeletal isomerization of the fragment PtCH2CR(CD2OMs)CH2 (6), to give [PtCH2CH2CR(CD2OMs)] (7), may occur in the absence of free pyridine for 3a** and 3c** but not in its presence and cannot occur for 3b**. Solvolysis of 6 gives exclusively (3c**) or largely (3a**, 3b**) the product labeled at C3 whereas solvolysis of 7 gives exclusively the product labeled at C1. Similarities with and differences between these reactions and the analogous organic ring expansions are discussed.
