Synthesis and resolution of (R*,R*)-(±)-1,1,4,7,10,10-hexaphenyl-1,10-diarsa-4,7-diphosphadecane:: New ligand for the stereoselective self-assembly of dicopper(I), disilver(I), and digold(I) helicates

Diphenylvinylarsine oxide reacts with 1,2-bis(phenylphosphino)ethane in the presence of potassium tert-butoxide to give the anti-Markovnikov product (R*,R*)-(+/-)/(R*,S*)-1,1,4,7,10,10-hexaphenyl-1,10-diarsa-4,7-diphosphadecane dioxide-1AsO,10AsO, which, upon reduction with HSiCl3/NEt3 in boiling acetonitrile, affords in 84% overall yield the di(tertiary arsine)-di(tertiary phosphine) (R*,R*)-(+/-)/(R,S)-diphars. After separation of the diastereomers by fractional crystallization, the (R,R)-() form of the ligand was resolved by metal complexation with (+)-di(mu-chloro)bis[(R)-1-[1-(dimethylamino)ethyl]-2-phenyl-C-2,N]dipalladium(II): (R,R)-diphars, mp 87-88 degreesC, has [alpha](D)(21) = -18.6 (c 1.0, CH2Cl2); (S,S)-diphars has [alpha](D)(21) = +18.4 (c 1.0, CH2Cl2). The crystal and molecular structures of the complexes (M)-[M-2{(R,R)-diphars}(2)](PF6)(2) (M = Cu, Ag, Au) have been determined: [M-(S-Cu,S-Cu)]-(-)-[Cu-2{(R,R)-diphars}(2)]-(PF6)(2), orthorhombic, P2(1)2(1)2(1) (No. 19), a = 16.084(3) Angstrom, b = 18.376(3) Angstrom, c = 29.149(6) Angstrom, Z = 4; [M-(S-Ag,S-Ag)]-(+)-[Ag-2{(R,R)-diphars}(2)](PF6)(2), triclinic, P1, a = 12.487(2) Angstrom, b = 12.695(4) Angstrom, c = 27.243(4) Angstrom, alpha = 92.06degrees, beta = 95.19degrees, gamma = 98.23degrees, Z = 2; [M-(S-Au,S-Au,)]-(-)-[Au-2{(R,R)-diphars}(2)](PF6)(2), orthorhombic, P2(1)2(1)2(1) (No. 19), a = 16.199(4) Angstrom, b = 18,373(4) Angstrom, c = 29.347(2) Angstrom, Z = 4. In the copper(I) and gold(I) helicates, each ligand strand completes 1.5 turns of an M helix in a parallel arrangement about the two chiral MAs2P2 stereocenters of S configuration. The unit cell of the silver(I) complex contains one molecule each of the parallel helicate of M configuration and the conformationally related double a.-helix of M configuration in which each ligand strand completes 0.5 turns of an M helix about two metal stereocenters of S configuration, Energy minimization calculations of the three structures with use of the program SPARTAN 5.0 gave results that were in close agreement with the core structures observed.