Organometallics 1983, 2, 141-143
141
Nucleophilic Attack on y*-Coordinated Dithio Acids by Hydride Ion. A Preliminary Step in the Formation of a Variety of Nickel Complexes Claudio Bianchini, Carlo Mealli, Andrea Meli, and Giancarlo Scapacci +
Istituto per lo Studio della Stereochimica ed Energetica dei Composti di Coordinazione, C.N.R., 50 132 Firenze, Italy Received June 14, 1982
The nickel(I1) complexes [(tripho~)Ni(S~CPEt~)](BPh~)~, [(triphos)Ni(S2CSMe)]BPh4, [ (triphos)Ni(S2COEt)]BPh4,and [(triphos)Ni(S2CNEt2)]BPh4 (triphos = 1,1,l-tris((diphenyphosphin0)methyl)ethane) react with NaBH, to give the complexes [(triphos)Ni(SzC(H)PEt3HBPh,,[ (triphos)Ni(?r-CS2)],[(triphos)Ni(CO)], and [ (triphos)Ni(SH)],respectively. The formation of all of these compounds is suggested to proceed via nucleophilic attack by the hydride ion from NaBH, on the electrophilic CS2carbon atom, followed by rearrangement of the resultant adduct. In some cases the reaction is accompanied by a lowering of the metal oxidation state by one or two units.
Introduction
Scheme I
Increasing attention has been directed recently toward the reactivity of (q2-dithio acidlmetal complexes (I) with nucleophiles. Reactions of V2-metal-linked S2C-X groups include ligand substitution to give complexes with different dithio acid and nucleophile addition to give 1,l-dithiolate c ~ m p l e x e s . ~The , ~ q2-coordination of dithio acid ligands enhances the electrophilicity of the CS2carbon atom, which consequently can be attacked by nucleophiles. In recent papers were showed that the hydride ion from NaBH, attacks the metal-coordinated S2C-PEt3zwitterion (11) and transforms it into the dithioformate or the phosphonium adduct of dithi~formate.’,~
nt
n
/>\
( tr I p hos ) N , I
->C-X
t
(2)
NaBH4
X = NElp, n
:1
(triphos)NlCO
(3)
(triphos )NiSH
(4)
Experimental Section I, L = ancillary ligand
I1
Now we show that the reactivity of (q2-dithioacid)metal complexes with NaBH, is in general a chemical feature of these disulfido ligands. The reactions of a number of nickel(I1) complexes of formula [ (triphos)Ni(S2C-X)](BPh,), (111) and NaBH, are summarized in Scheme I.
111, X = SMe, OEt, NEt,; n = 1 X = PEt,;n= 2
The product obtainable from each of these reactions depends on the nature of the X substituent. Beside addition reactions, the hydride ion may cause the fragmentation of the chelated dithioacid, thus generating metal complexes with a variety of smaller ligands such as CS2, CO, and HS-. These reactions are often accompanied by a decrease of the metal oxidation number by one or two units. (1) (a) Bianchini, C.; Meli, A.; Orlandini, A.; Scapacci, G. J.Organomet. Chem. 1981, 215, C59. (b) Bianchini, C.; Innocenti, P.; Meli, A.; Orlandini, A.; Scapacci, G. Ibid. 1982, 233, 233. (2) Bianchini, C.; Mealli, C.; Meli, A.; Scapacci, G. J . Chem. SOC., Dalton Trans. 1982, 799. (3) Fackler, J. P., Jr.; Seidel, W. C. Inorg. Chem. 1969, 8, 1631. (4) (a) Bianchini, C.; Meli, A.; Orlandini, A. Angew. Chem., Int. Ed. Engl. 1982, 21, 197. (b) Bianchini, C.; Meli, A.; Orlandini, A. Inorg. Chem., in press. (5) Bianchini, C.; Meli, A.; Nuzzi, F.; Dapporto, P. J . Organomet. Chem. 1982,236, 245.
All chemicals and solvents employed were reagent grade and were used without further purification. All the reactions described were carried out under an atmosphere of dry nitrogen. The solid complexes were collected on a sintered-glass frit and washed successively with ethanol and petroleum ether (bp 40-70 O C ) before being dried in a stream of dry nitrogen. Infrared spectra were recorded with a Perkin-Elmer 283 spectrophotometer using samples mulled in Nujol. 31PNMR spectra were taken on a Varian CFT 20 spectrometer. Chemical shifts are downfield (+) from external H3P04. The methods used for the magnetic and molar conductance measurements and the recording of the UV-visible spectra have been described previously.6 Syntheses. [(triphos)Ni(S2C(H)PEt3}]BPh4 (1). A solution of [ (triphos)Ni(SzCPEt3)] (BPh4)2(0.45 g, 0.3 mmol) in acetone (25 mL) was treated with NaBH4 (0.02 g, 0.5 mmol) in ethanol (10 mL). There was an immediate color change from dark green to orange. By addition of n-butanol(20 mL) to the solution and partial evaporation an orange microcrystalline solid was obtained; yield 85%. Anal. Calcd for C72H75BNiP4S2: C, 72.18; H, 6.31; Ni, 4.90; P, 10.34. Found: C, 71.97; H, 6.24; Ni, 4.85; P, 10.45. [(triphos)Ni(r-CS,)] (2). A solution of NaBH, in ethanol was added dropwise to a suspension of [(triphos)Ni(S,CSMe)]BPh: (0.34 g, 0.3 mmol) in acetone (30 mL) until the suspended compound dissolved to give a red brown solution. Ethanol (10 mL) then was added. Dark brown crystals precipitated in a short time: yield 90%; IR (cm-’) u(C=S) 1145, u(CS) 630. Anal. Calcd for C42H39NiP3S2: C, 66.41; H, 5.17; Ni, 7.73; S, 8.44. Found: C, 66.25; H, 5.14; Ni, 7.64; S, 8.35. (6) Sacconi, L.; Bertini, I.; Mani, F. Inorg. Chem. 1968, 7, 1417. (7) Unpublished results of this laboratory. The [(triphos)Ni(S2CSMe))BPh, complex was synthetized by treatment under nitrogen of a solution of [(triphos)Ni(S2CS)](0.5 mmol)2in CH2C12(20 mL) with MeOS02F (0.55 mmol), followed by addition of NaBPh, (0.5 mmol) in ethanol (30 mL).
0276-7333/83/2302-0141$01.50/0 0 1983 American Chemical Society
142 Organometallics, Vol. 2, No. 1, 1983
I 1
Lb
-LO
0 PP"
Figure 1. Variable-temperature31P(1H) NMR spectra of [ (triphos)Ni(S2C(H)PEt,)]BPh4in acetone. [(triphos)Ni(CO)](3). An acetone (30 mL) suspension of [(triphos)Ni(S,COEt)]BPh,s (0.34 g, 0.3 mmol) was treated with a large excess of NaBH, in ethanol (20 mL) which caused the solid to dissolve, giving a yellow brown solution. When left standing for 1 h, the solution gave yellow crystals: yield 50%; IR (cm-') v ( C 0 ) 1890. Anal. Calcd for C42H39NiOP3:C, 70.91; H, 5.52; Ni, 8.25. Found: C, 70.81; H, 5.60; Ni, 8.19. [(triphos)Ni(SH)](4). NaBH, (0.05 g, 1 mmol) in ethanol (20 mL) was allowed to react with a solution of [(triphos)Ni(SzCNEt.J]BPh4s(0.34 g, 0.3 mmol) in acetone (30 mL). Within a few minutes a light brown solution was obtained. Yellow crystals precipitated in a short time; yield 40%. Anal. Calcd for C4,H40NiP3S:C, 68.73; H, 5.62; Ni, 8.19; S, 4.47. Found: C, 68.68; H, 5.58; Ni, 8.12; S, 4.39.
Results and Discussion When NaBH, was reacted with [ (triphos)Ni(S2CPEt3)](BPh,)2 (triphos = l,l,l-tris((dipheny1phosphin0)methyl)ethane) in acetone-alcohol, the color of the solution turns to orange and a microcrystalline orange solid of empirical formula [ (triphos)Ni(S,C(H)PEt3)]BPh4(1) precipitates. This complex is diamagnetic and air stable in the solid state. It is soluble in all common organic solvents, in which it behaves as a 1:l electrolyte (molar conductance in nitroethane solution: 46 cm2 Q-' mol-'). The reflectance spectrum, with no band at frequencies
