Preparation of Palladium(I) and Platinum(I) Dinuclear Complexes
1. Preparation of [Pd2(CNMe)6][PF6]2
PdCl2 + 2NaCl → Na2PdCl4
Na2PdCl4 + (excess) CNMe → Pd2(CNMe)62+ + 2NaCl
Pd2(CNMe)62+ + (excess) NH4PF6 → [Pd2(CNMe)6][PF6]2 + NH4+
Procedure:
A solution of PdCl42- was prepared by dissolving PdCl2 (600 mg, 3.4 mmol) and NaCl (600 mg, 10.4 mmol) in 30 mL of water. Methyl isocyanide (0.8 mL, 13.5 mmol) was added and the brown solution immediately turned colorless. The clear solution was allowed to stand for 18 h during which time bubbles of a gas slowly evolved and a bright yellow color developed. A solution containing 1 g (6 mmol) of ammonium hexafluorophosphate was added and the pale yellow product precipitated immediately. The pure crystalline salt was obtained as an acetone solvate following recrystallization from acetone/2-propanol or from acetone/diethyl ether. Acetone-free material was produced by heating the product under vacuum at 60°C for 12 h (yield 70-80%).
Properties:
Formula weight 749.10 g mol-1; IR[KBr] à(CN) 2236 cm-1; 1H NMR (CD3CN) d 3.65.
Notes:
(a) Work in a hood.
(b) 10 h is usually a sufficient standing period (check for yellow color, no bubbles) - longer periods occasionally lead to plating Pd metal. If this happens, work up the solution anyway. The metal may be removed by filtering through Celite before recrystallization.
(c) Recrystallize from acetonitrile/diethyl ether to get acetone free product.
(d) Store product in a desiccator or under N2 (keep away from moisture).
References:
1. Boehm, J. R.; Doonan, D. J.; Balch, A. L. J. Am. Chem. Soc. 1976, 98, 4845.
2. Preparation of [Pt2(CNMe)6][BF4]2
K2PtCl4 + 2NaBF4 → Na2PtCl4 + 2KBF4
Na2PtCl4 + (excess) CNMe + (excess) NaBF4 → [Pt2(CNMe)6][BF4]2
Procedure:
Potassium tetrachloroplatinate(II) (830 mg, 2 mmol) was added to 10 mL of an aqueous solution saturated with sodium tetrafluoroborate. The mixture was stirred 15 min and filtered to remove the insoluble potassium tetrafluoroborate which formed. The filtrate was treated with methyl isocyanide (0.5 mL, 8.3 mmol) added dropwise with stirring. The pale yellow solution was allowed to stand for 24 h during which time the product formed as white crystals. The mixture was filtered and the solids were washed with water. The filtrate yielded a smaller second crop of crystals during the following 24 h. The combined crops were recrystallized from acetonitrile/ether (yield: 370 mg, 46%).
Data:
Formula weight 810.16 g/mol; IR[KBr] à(CN) 2242 cm-1; 1H NMR (CD3CN) d 3.51 (12 H), 3.33 (6 H).
Notes:
(a) Work in a hood.
(b) Keep solution volume under 10 mL - yield decreases with more dilute solutions.
(c) Add CH3NC very slowly.
(d) If no solid is formed after 24 h, then cool the solution in an ice bath.
(e) Do not expect a 46% yield - usually get about 30%.
(f) Store product in a desiccator or under N2 (keep away from moisture).
(g) Yields over 80% have been obtained when 5-7 mL of sat. NaBF4(aq) solution was used for 1.0 g K2PtCl4. The reaction was cropped first after 2 days stirring and cropped three more times over a course of 1-2 weeks.
References:
1. Boehm, J. R.; Doonan, D. J.; Balch, A. L. J. Am. Chem. Soc. 1976, 98, 4845.
3. Preparation of [PdPt(CNMe)6][PF6]2
[Pt(CNMe)4][PF6]2 + Pd2(dba)3.CHCl3 + 4CNMe → [PdPt(CNMe)6][PF6]2
Procedure:
Palladium chloride, 1.05 g (5.92 mmol), was added to hot (ca. 50°C) methanol, 150 mL, containing dba (dibenzylideneacetone) 4.60 g (19.6 mmol) and sodium acetate 3.90 g (47.5 mmol). The mixture was stirred for 4 h at 40°C to give a reddish-purple precipitate and allowed to cool to complete the precipitation. The precipitate was collected by filtration, washed successively with water and acetone and dried in vacuo. The precipitate, 3.39 g, was dissolved in hot chloroform, 120 mL, and filtered to give a deep violet solution. To the solution, diethyl ether, 170 mL, was added slowly. Deep purple needles precipitated. These were removed by filtration, washed with diethyl ether, and dried in vacuo. The complex, m.p. 122-124° dec., satisfying the composition of Pd2(dba)3(CHCl3) was obtained in 80% yield.
Methyl isocyanide (0.32 mL) was added to a filtered solution of 0.313 g of potassium tetrachloroplatinate in 10 mL of water. Immediately a filtered solution of 0.60 g of ammonium hexafluorophosphate in 10 mL of methanol was added. The white precipitate, which rapidly formed, was collected by filtration, washed with water, and vacuum dried. Purification was achieved by recrystallization from acetonitrile, yield 95%: conductivity K0.001 M = 181 cm2 mol-1 ohm-1 (nitromethane); IR [KBr] à(CN) 2308 cm-1; 1H NMR [CD3CN] d 3.68(s).
To a solution of 125.4 mg (0.193 mmol) of [(CH3NC)4Pt][PF6]2 in 10 mL of acetonitrile was added successively 0.25 mL of methyl isocyanide and 100 mg (0.097 mmol) of solid Pd2(dba)3.CHCl3. The mixture was heated briefly until the solid dissolved to give a clear yellow solution. After filtering, the white product was obtained by addition of diethyl ether and purified by dissolution in acetone and re-precipitation with diethyl ether; yield 94%.
Properties:
Formula weight 837.79 g/mol; IR [KBr] à(CN) 2231 cm-1; 1H NMR [CD3CN] d 3.55 (6 H), 3.44 (9 H), 3.38 (3 H).
References:
1. Boehm, J. R.; Doonan, D. J.; Balch, A. L. J. Am. Chem. Soc. 1976, 98, 4845.
2. Ukai, T.; Kawazwra, H.; Ishii, Y. J. Organomet. Chem., 1973, 65, 253.
3. Miller, J.; Balch, A. Inorg. Chem. 1972, 11, 2069.