Syntheses, Structures, and Thermal Properties of Gyroscope-like Complexes Consisting of PtCl2 Rotators Encased in Macrocyclic Dibridgehead Diphosphines P((CH2)n)3P with Extended Methylene Chains (n = 20/22/30) and Isomers Thereof

Abstract

Reactions of P((CH2)mCH═CH2)3 (2.0 equiv; m = 9 (f), 10 (g), 14 (k)) and PtCl2 in toluene give trans-PtCl2(P((CH2)mCH═CH2)3)2 (trans-1f,g,k; 63–49%). Reactions of trans-1f,g with Grubbs first generation catalyst (CH2Cl2/reflux) followed by hydrogenations (cat. PtO2) afford chromatographically separable gyroscope-like trans-PtCl2(P((CH2)n)3P) (trans-2f,g, 3–19%; from interligand metathesis) and trans-PtCl2(P((CH2)n−1CH2)(CH2)nP((CH2)n−1CH2)) (trans-2′f,g, 25–12%; from inter- and intraligand metathesis), where n = 2m + 2. Under analogous conditions, trans-1k gives only cis-PtCl2(P((CH2)30)3P) (cis-2k, 39%), but when o-C6H4Cl2 solutions are kept at 180 °C, trans-2k forms (quantitative by 31P NMR; 72% isolated). In contrast, a similar sequence with the Hoveyda–Grubbs second generation catalyst gives only trans-2k (8%). The stability order cis > trans is established for 1g and 2′f,g in CH2Cl2 (61–56:39–44; months at RT), but the opposite is found for 1g and 2′f in toluene (9–7:91–93) or 2′f in o-C6H4Cl2 (7:93). Thus, it is proposed that the conversion of trans-1k to cis-2k involves a geometrical isomerization of the educt or an intermediate catalyzed by a species derived from Grubbs catalyst. The crystal structures of trans-2g·THF and cis-2′f,g are determined and analyzed in detail.