Syntheses and structures of square planar diplatinum butadiynediyl complexes with two different monophosphine ligands on each terminus; probing the feasibility of a new type of inorganic atropisomerism
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2017 Elsevier B.V. Reactions of trans-(C6F5)(p-tol3P)2Pt(Cl) (PtCl) and R2PhP (1.0 equiv; R = a/Me, b/p-t-BuC6H4, c/p-MeOC6H4, d/n-Pr; CH2Cl2/rt (a) or toluene/reflux (b-d)) give mainly trans-(C6F5)(R2PhP)(p-tol3P)Pt(Cl) (PtCl-a-d, 89-29%) and some disubstitution products trans-(C6F5)(R2PhP)2Pt(Cl) (PtCl-a-d, 413%). No substitution occurs with t-Bu2PhP. However, (cod)(C6F5)Pt(Cl) and t-Bu2PhP (2.7 equiv; toluene/reflux) react to give trans-(C6F5)(t-Bu2PhP)2Pt(Cl) (PtCl-e, 64%), which upon treatment with p-tol3P (1.0 equiv, toluene/reflux) yields trans-(C6F5)(t-Bu2PhP)(p-tol3P)Pt(Cl) (PtCl-e, 91%). Additions of excess butadiyne to PtCl-a-d (CH2Cl2, cat. CuI, HNEt2) afford the butadiynyl complexes trans-(C6F5)(R2PhP)(p-tol3P)Pt(CC)2H (PtC4H-a-d, 3677%), but PtCl-e does not similarly react. Cross couplings of PtCl-a-c and PtC4H-a-c (cat. CuI, HNEt2) give mixtures of diplatinum butadiynyl complexes in which the two unlike phosphine ligands scramble over all four positions (PtC4Pt, PtC4Pt-a-c, PtC4Pt-a-c, PtC4Pt-a-c, PtC4Pt-a-c, PtC4Pt-b; TLC separable, 27-2% each). A modified coupling recipe is tested with PtCl-b,d and PtC4H-b,d (t-BuOK, KPF6, cat. CuCl), and gives PtC4Pt-b,d (2176%) with only traces of scrambling. Crystal structures of PtCl-e, PtC4H-a, PtC4Pt-a-d, and PtC4Pt-b are determined, and the endgroup/endgroup interactions analyzed. Low temperature NMR spectra do not reveal any dynamic processes.
