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The ligand Ph2PC(CH3)2PPh2 (2,2-dppp) reacts with Ni(II) salts to give robust square-planar chelate complexes [NiX2(2,2-dppp-P,P‘)] (X = Cl, 1; X = Br, 2) and the salt [Ni(2,2-dppp)2](ClO4)2 (3). The Pd(II) analogues [PdCl2(2,2-dppp)] (4), [PdI2(2,2-dppp)] (5), and [Pd(2,2-dppp)2](BF4)2 (6) have also been made. The crystal structure of 5 (obtained as 5·0.8CH2Cl2) has been determined by X-ray diffraction. The geminal C(CH3)2 group, when compared with related Ph2PCH2PPh2 (dppm) complexes, causes a small compression of the P−C−P chelate ring angle (to 91.3(3)° for 5). With [PtCl2(PhCN)2], 2,2-dppp affords [PtCl2(2,2-dppp)] (7), which undergoes metathesis with NaI to give [PtI2(2,2-dppp)] (8), and [Pt(2,2-dppp)2]Cl2 (9) was obtained by reaction of [PtCl2(PhCN)2] with 2 equiv of 2,2-dppp. Reactions were then attempted with 7 and 9, which are known to result in ring-opening reactions with the corresponding complexes of dppm, but in all cases, only 2,2-dppp chelate complexes could be isolated. Thus, treatment of 7 or 9 with excess MeLi gave exclusively [PtMe2(2,2-dppp)] (10) rather than cis,cis-[Pt2Me4(2,2-dppp)2]. Attempts to ring-open 10 with excess 2,2-dppp to give cis-[PtMe2(2,2-dppp−P)2] were unsuccessful. Treatment of 10 with 1 equiv of HCl or, better, treatment of [PtCl(Me)(1,5-cyclooctadiene)] with 2,2-dppp gave only mononuclear [PtCl(Me)(2,2-dppp)] (11) and no dimer of the type [MePt(μ-2,2-dppp)2(μ-Cl)PtMe]Cl. Treatment of 7 with 2 equiv of NaCN in EtOH gave the chelate complex [Pt(CN)2(2,2-dppp)] (12) rather than trans,trans-[Pt2(CN)4(μ-2,2-dppp)2], and treatment of 7 with LiC⋮CPh in thf or (better) H2NNH2·H2O/HC⋮CPh in EtOH gave [Pt(C⋮CPh)2(2,2-dppp)] (13), rather than trans,trans-[Pt2(C⋮CPh)4(μ-2,2-dppp)2]. Reaction of 7 with LiC⋮CBun in thf likewise gave [Pt(C⋮CBun)2(2,2-dppp)] (14) in low yield. The complexes were characterized by microanalyses (C, H, N and, in some cases, halide), infrared spectroscopy, 31P{1H} and 1H NMR spectroscopy, and fast atom bombardment mass spectrometry.

The ligand (Ph 2 P) 2 CdCH 2 (dppen) reacts with [RuCl 2 (PPh 3 ) 3 ] in CH 2 Cl 2 to give trans-[RuCl 2 (dppen) 2 ], 1. Complex 1 has reversible Ru(II)/Ru(III) electrochemistry, and on treatment with NOBF 4 , 1 affords [RuCl 2 (dppen) 2 ]BF 4 , 1 + . Refluxing solutions of 1 in chlorobenzene affords cis-[RuCl 2 (dppen) 2 ], 2. With excess RNH 2 in chlorobenzene or toluene, 1 reacts to give functionalized diphosphine complexes of general formula trans-principally by a small upfield shift in their 31 P{ 1 H} NMR spectra compared to that of 1 and by their distinctive 1 H NMR spectra. Complex 3b‚4MeOH crystallizes in the space group P1 h with a ) 11.448(6) Å, b ) 13.10(1) Å, c ) 11.178(7) Å, R ) 93.16(6)°, β ) 99.51(5)°, γ ) 92.19(5)°, V ) 1648(2) Å 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 acetonitriletetraethylammonium 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 LiCtC(CH 2 ) 3 -CH 3 , 1 reacts to give trans-[Ru(CtCR) 2 ({Ph 2 P} 2 CHCH 2 CtCR) 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-[RuCl 2 ({Ph 2 P} 2 CHCH 2 NHR) 2 ] (R: n-hexyl, 4a; [CH 2 ] 3 Si[OEt] 3 , 4b). However, 4b was too insoluble for electrode derivatization. The "half-sandwich" complex [CpRuCl(dppen)] (6; Cp ) η 5 -C 5 H 5 ) also reacts with RNH 2 to give [CpRuCl({PPh 2 } 2 CHCH 2 NHR)] (R: -[CH 2 ] 3 NH 2 , 7a; -CH 2 Ph, 7b).

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A method for preparing bidentate phosphine complexes functionalised for oxide surface modification is developed utilising the chemistry of a coordinated diphosphine; a redox-active ruthenium(ii) complex is anchored to indium-doped tin oxide (ITO) surfaces, and the extent of coverage is determined using cyclic voltammetry.