Nucleophilic addition to complexes of (Ph2P)2C=CH2 as a route to functionalized, redox-active ruthenium(II)-diphosphine complexes

The ligand (Ph2P)(2)C=CH2 (dppen) reacts with [RuCl2(PPh3)(3)] in CH2Cl2 to give trans-[RuCl2(dppen)(2)], 1. Complex 1 has reversible Ru(II)/Ru(III) electrochemistry, and on treatment with NOBF4, 1 affords [RuCl2(dppen)(2)]BF4, 1(+). Refluxing solutions of 1 in chlorobenzene affords cis-[RuCl2(dppen)(2)], 2. With excess RNH2 in chlorobenzene or toluene, 1 reacts to give functionalized diphosphine complexes of general formula trans-[RuCl2({Ph2P}(2)CHCH2NHR)(2)] (R: PhCH2, 3a; [CH2](3)NH2, 3b; n-octyl, 3c; R-alpha-CH(Me)Ph, 3d; [CH2](3)Si(OEt)(3), 3e) characterized principally by a small upfield shift in their P-31{H-1} NMR spectra compared to that of 1 and by their distinctive H-1 NMR spectra. Complex 3b . 4MeOH crystallizes in the space group P (1) over bar with a = 11.448(6) Angstrom, b = 13.10(1) Angstrom, c = 11.178(7) Angstrom, alpha = 93.16(6)degrees, beta = 99.51(5)degrees, gamma = 92.19(5)degrees, V = 1648(2) Angstrom(3), and D-calcd = 1.250 g cm(-3) for Z = 1. Complex 3e reacts with the surface hydroxyl groups of indium-doped tin oxide (ITO) electrodes, to give monolayers of anchored, redox-active Ru(II)-diphosphine complexes, characterized by cyclic voltammetry. The modified electrodes are stable to repetitive cycling over the Ru(II)/Ru(III) redox wave in acetonitrile-tetraethylammonium tetrafluoroborate and in aqueous buffer (pH 8). With anodized Pt electrodes, however, 3e reacts to form multilayers. Reaction of 1 with secondary amines is more sluggish than reaction with primary amines, and only adducts with pyrrolidine (3f) and morpholine (3g; impure) were isolated. With LiC=C(CH2)(3)CH3, 1 reacts to give trans-[Ru(C=CR)(2)({Ph2P}(2)CHCH2C=CR)2] (R = n-butyl, 5); acetylide nucleophiles displace the chloride ligands as well as adding to the dppen double bonds of 1. Other carbanions fail to react with 1. The cis complex 2 reacts with a limited range of primary amines, to afford cis-[RuCl2({Ph2P}(2)CHCH2NHR)(2)] (R: n-hexyl, 4a; [CH2](3)Si[OEt](3), 4b). However, 4b was too insoluble for electrode derivatization. The "half-sandwich" complex [CpRuCl(dppen)] (6; Cp = eta(5)-C5H5) also reacts with RNH2 to give [CpRuCl({PPh2}(2)CHCH2NHR)](R: -[CH2](3)NH2, 7a; -CH2Ph, 7b).