Monophosphine and diphosphine ligands for diplatinum polyynediyl complexes: Efficient syntheses of new functionality-containing systems and model compounds

Br(CH₂)₄Br and NaO(CH₂)₂CHCH₂ react under suitable conditions to give Br(CH₂)₄O(CH₂)₂CHCH₂ (55%), which is treated with KPPh₂ to yield the ether-containing phosphine Ph₂P(CH₂)₄O(CH₂)₂CHCH₂ (83%). The reaction of CH₃CH₂OC(O)CHC(CH₃)₂ and BrMg(CH₂)₃CHCH₂ in the presence of CuCl (cat.) and ClSiMe₃ yields CH₃CH₂OC(O)CH₂C(CH₃)₂(CH₂)₃CHCH₂ (67%), which is reduced to an alcohol that is brominated, reacted with Grubbs’ catalyst, hydrogenated, and treated with KPPh₂ to give the bis(geminally dimethylated) diphosphine Ph₂P(CH₂)₂C(CH₃)₂(CH₂)₈C(CH₃)₂(CH₂)₂PPh₂ (47% overall). The photochemical reaction of I(CF₂)₈I and H₂CCHCH₂SnBu₃ yields H₂CCHCH₂(CF₂)₈CH₂CHCH₂ (52%), which is converted with 9-BBN to a diol (92%) that is brominated and treated with LiPR₂ to give the fluorinated diphosphines R₂P(CH₂)₃(CF₂)₈(CH₂)₃PR₂ (R = a, p-tol, 67%; b, t-Bu, 69%; c, o-tol, 86%). Reactions of Br(CH₂)_mBr and LiPR₂ similarly yield R₂P(CH₂)_mPR₂ (m/R = 8/a, 95%; 14/a, 96%; 14/p-C₆H₄-t-Bu, 98%). Reactions of KPPh₂ with Br(CH₂)_m′CHCH₂and Br(CH₂)₇CH₃ give the corresponding monophosphines Ph₂P(CH₂)_m′CHCH₂ (m′ = 7, 82%; 10, 84%) and Ph₂P(CH₂)₇CH₃ (85%). When the former is combined with [Pt(μ-Cl)(C₆F₅)(tht)]₂ (tht = tetrahydrothiophene), trans-(C₆F₅)(Ph₂P(CH₂)_m′CHCH₂)₂PtCl (77-70%) is isolated. When the latter (excess) is combined with trans,trans-(C₆F₅)(p-tol₃P)₂Pt(CC)₄Pt(Pp-tol₃)₂(C₆F₅) (RT, 65 °C), trans,trans-(C₆F₅)(Ph₂P(CH₂)₇CH₃)₂Pt(C C)₄Pt(Ph₂P(CH₂)₇CH₃)₂(C₆F₅) (53%) is isolated.     

sp carbon chains surrounded by sp(3) carbon double helices: directed syntheses of wirelike Pt(CC)(n)Pt moieties that are spanned by two P(CH(2))(m)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(CC)2H (HNEt2, cat. CuI) give trans-(C6F5)(Ph2P(CH2)m'CH=CH2)2Pt(CC)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(CC)4Pt(Ph2P(CH2)m'CH=CH2)2(C6F5) (4a-d, 64-84%). Treatment of 3c-e with excess HCCSiEt3 under Hay conditions gives trans-(C6F5)(Ph2P(CH2)m'CH=CH2)2Pt(CC)3SiEt3 (56-73%). Homocouplings (n-Bu4N+ F-, Me3SiCl, Hay conditions) afford trans,trans-(C6F5)(Ph2P(CH2)m'CH=CH2)2Pt(CC)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 trans,trans-(C6F5)(Ph2P(CH2)mPPh2)Pt(CC)nPt(Ph2P(CH2)mPPh2)(C6F5) with termini-spanning diphosphines and trans,trans-(C6F5)(Ph2P(CH2)mPPh2)Pt(CC)nPt(Ph2P(CH2)mPPh2)(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)mPPh2)PtCl (49-59%), followed by analogous introductions of (CC)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.     

sp carbon chains surrounded by sp(3) carbon double helices: coordination-driven self-assembly of wirelike Pt(CC)(n)Pt moieties that are spanned by two P(CH(2))(m)P linkages

Reactions of trans,trans-(C6F5)(p-tol3P)2Pt(CC)4Pt(Pp-tol3)2(C6F5) and diphosphines Ar2P(CH2)mPAr2 yield trans,trans-(C6F5)(Ar2P(CH2)mPAr2)Pt(CC)4Pt(Ar2P(CH2)mPAr2)(C6F5), in which the platinum atoms are spanned via an sp and two sp3 carbon chains (Ar/m = 3, Ph/14, 87%; 4, p-tol/14, 91%; 5, p-C6H4-t-Bu/14, 77%; 7, Ph/10, 80%; 8, Ph/11, 80%; 9, Ph/12, 36%; only oligomers form for m > 14). Crystal structures of 3-5 show that the sp3 chains adopt chiral double-helical conformations that shield the sp chain at approximately the van der Waals distance, with both enantiomers in the unit cell. The platinum square planes define angles of 196.6 degrees -189.9 degrees or more than a half twist. Crystal structures of 7-9, which have shorter sp3 chains, exhibit nonhelical conformations. Reaction of the corresponding Pt(CC)6Pt complex and Ph2P(CH2)18PPh2 gives an analogous adduct (27%). The crystal structure shows two independent molecules, one helical and the other not. Low-temperature NMR data suggest that the enantiomeric helical conformations of 3-5 rapidly interconvert in solution. Cyclic voltammograms of 3-5 show more reversible oxidations than model compounds lacking bridging sp3 chains. These are the only double-helical molecules that do not feature bonding interactions between the helix strands, or covalent bonds to templates dispersed throughout the strands, or any type of encoding. The driving force for helix formation is analyzed.     

Wire-like PtC[triple bond]CC[triple bond]CC[triple bond]CC[triple bond]CPt moieties surrounded by double-helical "insulation": new motifs featuring P(CH2)20P and P(CH2)4O(CH2)2O(CH2)4P linkages

Ring-closing alkene metatheses of trans,trans-(C6F5)(Ph2P-Z-CH=CH2)2Pt(C[triple bond]C)4Pt(Ph2P-Z-CH=CH2)2(C6F5) (Z = (CH2)9, (CH2)4O(CH2)2), followed by hydrogenation, give the title compounds; the former exhibits an exceptionally twisted conformation, and the latter establishes that functional groups can be incorporated into the flexible sp3 chain.