sp carbon chains surrounded by sp3 carbon double helices:: Directed syntheses of wirelike Pt(CC)nPt moieties that are spanned by two P(CH2)mP linkages via alkene metathesis

Reactions of trans-(C6F5)(Ph2P(CH2)(m')CHCH2)(2)PtCl (1; m' = a, 6; b, 7; c, 8; d, 9; e, 10) and H(CC)(2)H (HNEt2, cat. CuI) give trans-(C6F5)(Ph2P(CH2)(m')CHCH2)(2)Pt(CC)(2)H (3a-e, 80-95%). Oxidative homocouplings of 3a-d under Hay conditions (O-2, cat. CuCl/TMEDA, acetone) yield trans,trans-(C6F5)(Ph2P(CH2)(m')CHCH2)(2)Pt(CC)(4)Pt(Ph2P(CH2)(m')CHCH2)(2)(C6F5) (4a-d, 64-84%). Treatment of 3c-e with excess HCCSiEt3 under Hay conditions gives trans-(C6F5)(Ph2P(CH2)(m')CHCH2)(2)Pt(CC)(3)SiEt3 (56-73%). Homocouplings (n-Bu4N+ F-, Me3SiCl, Hay conditions) afford trans,trans-(C6F5)(Ph2P(CH2)(m')CHCH2)(2)Pt(CC)(6)Pt(Ph2P(CH2)(m')CHCH2)(2)(C6F5) (13c-e, 59-64%). Reactions of 4a-d and 13c-e with Grubbs' catalyst, followed by hydrogenation, give mixtures of trans,trans-(C6F5)(Ph2P(CH2)(m)PPh2)Pt(CC)(n)Pt(Ph2P(CH2)(m)PPh2)(C6F5) with termini-spanning diphosphines and trans,trans-(C6F5)(Ph2P(CH2)(m)PPh2)Pt(CC)(n)Pt(Ph2P(CH2)(m)PPh2)(C6F5) with trans-spanning diphosphines (m = 2m' + 2; n = 4, 6). The latter (n = 4) are independently synthesized by similar metatheses/hydrogenations of 1a-d to give trans-(C6F5)(Ph2P(CH2)(m)PPh2)PtCl (49-59%), followed by analogous introductions of (CC)(4) chains (66-77%). Crystal structures of complexes with termini-spanning diphosphines show sp(3) chains with both double-helical (m/n = 20/4) and nonhelical (m/n = 20/6) conformations, and highly shielded sp chains. The sp(3) chains of complexes with trans-spanning diphosphines exhibit double half-clamshell conformations. The dynamic properties of both classes of molecules are analyzed in detail.