sp Carbon Chains Surrounded by sp³ Carbon Double Helices: Directed Syntheses of Wirelike Pt(C⋮C)<i>_n</i>Pt Moieties That Are Spanned by Two P(CH₂)<i>_m</i>P Linkages via Alkene Metathesis

Reactions of trans-(C6F5)(Ph2P(CH2)m‘CHCH2)2PtCl (1; m‘ = a, 6; b, 7; c, 8; d, 9; e, 10) and H(C⋮C)2H (HNEt2, cat. CuI) give trans-(C6F5)(Ph2P(CH2)m‘CHCH2)2Pt(C⋮C)2H (3a−e, 80−95%). Oxidative homocouplings of 3a−d under Hay conditions (O2, cat. CuCl/TMEDA, acetone) yield trans,trans-(C6F5)(Ph2P(CH2)m‘CHCH2)2Pt(C⋮C)4Pt(Ph2P(CH2)m‘CHCH2)2(C6F5) (4a−d, 64−84%). Treatment of 3c−e with excess HC⋮CSiEt3 under Hay conditions gives trans-(C6F5)(Ph2P(CH2)m‘CHCH2)2Pt(C⋮C)3SiEt3 (56−73%). Homocouplings (n-Bu4N+ F-, Me3SiCl, Hay conditions) afford trans,trans-(C6F5)(Ph2P(CH2)m‘CHCH2)2Pt(C⋮C)6Pt(Ph2P(CH2)m‘CHCH2)2(C6F5) (13c−e, 59−64%). Reactions of 4a−d and 13c−e with Grubbs' catalyst, followed by hydrogenation, give mixtures of with termini-spanning diphosphines and 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)mPPh2)PtCl (49−59%), followed by analogous introductions of (C⋮C)4 chains (66−77%). Crystal structures of complexes with termini-spanning diphosphines show sp3 chains with both double-helical (m/n = 20/4) and nonhelical (m/n = 20/6) conformations, and highly shielded sp chains. The sp3 chains of complexes with trans-spanning diphosphines exhibit double half-clamshell conformations. The dynamic properties of both classes of molecules are analyzed in detail.