Nickel thioether chemistry: synthesis, structures and electrochemistry of five-co-ordinate nickel(II) complexes of [9]aneS3. Crystal structures of [Ni([9]aneS3)-(dppm)][PF6]2′, [Ni([9]aneS3)(dcpe)][PF6]2·1.25MeCN and [Ni([9]aneS3)(tdpme)][PF6]2{[9]aneS3= 1,4,7-Trithiacyclononane, dppm = Ph2PCH2PPh2′, dcpe =(C6H11)2–PC2H4P(C6H11)2′, tdpme = CH3C(CH2PPh2)3}

Abstract

Reaction of [Ni(L–L)Cl₂]{L–L = Ph₂PCH₂PPh₂(dppm), R₂PCH₂CH₂PR₂[R = Ph (dppe), C₆H₁₁(dcpe) or Me (dmpe)], cis-Ph₂PCHCHPPh₂(dppv), Ph₂PCH₂CH₂CH₂PPh₂(dppp) or MeC(CH₂PPh₂)₃(tdpme)} with 1 molar equivalent of 1,4,7-trithiacyclononane([9]aneS₃) afforded the complex cations [Ni([9]aneS₃)(L–L)]²⁺. The crystal structures of [Ni([9]aneS₃)(dppm)][PF₆]₂, [Ni([9]aneS₃)(dcpe)][PF₆]₂·;1.25MeCN and [Ni([9]aneS₃)(tdpme)][PF₆]₂ showed five-co-ordinate complexes with distorted square-pyramidal geometries about the nickel(II) centres with the S-donors of [9]aneS₃ occupying two basal and the apical position, Ni–S_apical 2.40–2.65 Å, Ni–P_basal 2.17–2.22 Å. The complex [Ni([9]aneS₃)(dppm)][PF₆]₂ crystallises in triclinic space group P, a= 10.9748(25), b= 13.9702(20), c= 15.7688(24)Å, α= 80.071(7), β= 70.817(8), γ= 76.441(8)°, D_c= 1.374 g cm^–3, Z= 2; [Ni([9]aneS₃)(dcpe)][PF₆]₂·;1.25MeCN crystallises in triclinic space group P, a= 12.432(8), b= 13.382(4), c= 15.070(6)Å, α= 86.83(2), β= 70.47(2), γ= 77.28(2)°, D_c= 1.445 g cm^–3, Z= 2; [Ni([9]aneS₃)(tdpme)][PF₆]₂ crystallises in monoclinic space group Cc, a= 10.7597(16), b= 37.399(5), c= 13.104(3)Å, β= 103.746(11)°, D_c= 1.491 g cm^–3, Z= 4. Cyclic voltammetry of the complexes [Ni([9]aneS₃)(L–L)][PF₆]₂ in MeCN (0.1 mol dm^–3 NBu₄PF₆) at 293 K at platinum electrodes showed one chemically reversible and one quasi-reversible one-electron reduction at ¹E_1/2=–0.77 to –1.16 V, ¹E_p= 61–92 mV, ²E_1/2=–1.31 to –1.93 V vs. ferrocene–ferrocenium. On the basis of ESR and electronic spectroscopy, these reduction products are assigned as pyraidal d⁹ nickel(I)[Ni([9]aneS₃)(L–L)]⁺ with binding of both P-donors retained, and tetrahedral d¹⁰ nickel(0)[Ni([9]aneS₃)(L–L)]⁰ species respectively. The reaction of [Ni([9]aneS₃)(L–L)]⁺ with CO in MeCN is discussed.