COORDINATION CHEMISTRY, REACTIVITIES AND STEREOCHEMISTRY OF NOVEL POLYDENTATE SULFINYL-SUBSTITUTED PHOSPHINES AND ARSINES

Abstract

The tridentate sulfinyl-substituted ligands (Ph2ECH2CH2)2SO (E-S(O)-E; E = As, P) and Ph2AsCH2CH2S(O)CH2CH2PPh2 (As-S(O)-P) have been prepared. The thermal stabilities and coordination chemistry of the three ligands were studied. The tridentate ligands E-S(O)-E' (E, E' = As, P) form square planar palladium(II) and platinum(II) complexes. In [PdBr2{P-S(O)-P-P,P'}h, P-S(O)-P behaves as a bridging bidentate diphosphine. In polar solvents, the complex undergoes ligand redistribution to form its monomeric analogue [PdBr{P-S(O)-P-P,P',S}]Br. The monomer-dimer interconversion is reversible in solution. However, only the dipalladium complex is isolated in solid state. In contrast, P-S(O)-P only forms a monomeric complex, [PtCl{P-S(O)-P-P,P',S}]CI, with a platinum(II) dichloride precursor. Ion pairing was detected for the complex in nonpolar solvents. Both [PdBr2{P-S(O)-P-P,P')]2 and [PtCl{P-S(O)-P-P,P',S}]Cl were characterized by X-ray crystallographic analyses. Complexes [MCl{E-S(O)-E-E,E',S}]CIO4 (M = Pd, E = As, P; M = Pt, E = P) and [PdCl{As-S(O)-P-As,P,S}]CIO4 were prepared. 1H NMR analysis on these palladium complexes revealed the stereochemical rigidity of the ring conformations adopted by the ligands E-S(O)-E (E = As, P) and As-S(O)-P in solution. To study the stereoelectronic effects on sulfoxide-metal bonding, complexes [ML{P-S(O)-PP,P ',S} ](ClO4)2 (M= Pd, Pt; L = CH3CN, PPh3, P(OEt)3) were obtained. Crystallographic analysis on [M {P(OEt)3} { P-S(O)-P-P,P',S} ](ClO4)2 showed slight pyramidal distortion of the coordination plane. Non-bonded interactions between the phosphite and its cis ligating groups were revealed. Ligand P-S(O)-P forms binuclear annular complexes, [M{P-S(O)-PP,P'}]22+ (M = Ag, Au), and linear chain, [(AuCl)2{ P-S(O)-P-P,P')], with two-coordinate silver(l) and gold(]). Four-coordination was observed for the binuclear species [Ag(µ-Cl){P-S(O)-P-P,P'}]2 which involves bridging chloro groups and PS(O)-P ligands. In our silver(I) and gold(I) complexes, P-S(O)-P coordinates to the two metals as a bridging ligand solely via the phosphorus donors. Palladium(II) complexes of (R)-N,N-dimethyl-1-(1-naphthyl)ethylamine are used as metal promoters for the asymmetric Diels-Alder reaction between l-phenyl-3,4- dimethylphosphole and divinyl sulfoxide to give the bidentate ligand, syn,exo-2,3 dimethyl-7-phenyl-5-vinylsulfinyl-7-phosphabicyclo[2.2.1]hept-2-ene (P-S(O)). Two optically active diastereomeric Diels-Alder adducts [Pd{ (R)-MeCH(1-C10H6)NMe2- C,N}{ (RS)-P-S(O)-O,P} ]ClO4 ((RS)-83) and [Pd{ (R)-MeCH(1-C10H6)NMe2- C,N}( (SS)-P-S( O )-O, P}] ClO4 ((SS)-83) were generated. Differing in the stereochemistry at the sulfur centers, the ligands share the same absolute configurations at P, C-1, C-4 and C-5 stereogenic centers, i.e. S, S, Sand R respectively, as a result of ?-facial stereoselectivity in the cycloaddition reaction. Complexes (RS)-83 and (SS)-83 extract free chlorides to form [PdCl( (R)- MeCH(1-C10H6)NMe2-C,N}{ (RS)-P-S(O)-P}] ((RS)-80) and [PdCl{ (R)-MeCH(1-C10H6)NMe2-C,N }{ (SS)-P-S(O)-P)] ((SS)-80), respectively, which involve monodentate P-S(O) ligands. Upon chloride abstraction, (RS)-80 and (SS)-80 revert to (RS)-83 and (SS)-83 respectively with the formation of six-membered P-O rings. Upon refluxing with cone HCl, (RS)-83 and (SS)-83 were transformed to [PdCl{ P-S-P,µS)}]2 (92; P-S = syn, exo-2,3-dimethyl-7-phenyl-5-thiolato-7- phosphabicyclo[2.2.1]hept-2-ene). For full characterization of 92, the readily crystallized [Pd{P-S-P,µS}{AsPh3}]2(ClO4)2 (94) was prepared. Molecular structures and stereochemistry of complexes (RS)-83, (SS)-83, (RS)-80 and 94 were determined by crystallographic analyses. Two twelve-membered quadridentate macrocycles PhE(CH2CH2SCH2CH2)2SO (ES2S(O); E = As, P) were synthesized by cyclization of PhE(CH2CH2SH)2 and (ClCH2CH2)2SO via cesium salt assistance. The macrocycles ES2S(O) display geometrical isomerism at the sulfinyl sulfur centers and the E donors. Macrocycle PS2S (O) undergoes slow oxygen migration in solution to form PhP(O)(CH2CH2SCH2CH2)2S. Benzylation was performed on the macrocycles for the study on their geometrical isomerism. Some nickel(II), palladium(II) and gold(I) complexes of the macrocycles were prepared.