Experimental
General. All the reactions were routinely carried out using standard Schlenk line techniques under an atmosphere of pure nitrogen. The solvents used were dry and free of oxygen. The compounds [Pd2(u-Br)2(PBut3)2] and [Pd2(u-I)2(PBut3)2] were prepared according to literature procedures.3 Other reagents were used as obtained from commercial sources. Infrared spectra were recorded in a Perkin-Elmer 1720 Infrared Fourier Transform Spectrometer between 4000 and 250 cm-1 as KBr pellets. 1H and 31P-{1H} NMR spectra were recorded on a JEOL JNM-EX270 Fourier Transform NMR spectrometer operating at a frequency of 290 MHz with chemical shifts reported relative to TMS and H3PO4 respectively. Mass spectra were recorded by Mr. J. Barton at Imperial College on a VG AutoSpec-Q as FAB using 3-NBA as matrix. Microanalyses (C, H, N) were carried out by Miss H. O'Callaghan at Imperial College.
Syntheses
Reaction of [Pd2(u-Br)2(PBut3)2] with CO
a) CO was bubbled for 10 minutes through a solution of [Pd2(u-Br)2(PBut3)2] (0.09 g, 0.12 mmol) in toluene. The green colour of the original reaction mixture changed immediately to dark orange. The reaction was stirred under a CO atmosphere for 2 hrs. The solvent was removed under reduced pressure and the remaining dark solid washed three times with hexane. An orange product partially soluble in hexane, was extracted from the bulk solid and recrystallised fromt a toluene/hexane mixture at 4[ring]C. This crystalline product was characterised as [Pd4(u-Br)3(u-CO)2((But3)2PMe2CH2(PBut3)3]. Elemental Analyses: found C 36.1%, H 5.9%, required C38H80Br3O2P3Pd4.0.5[C7H8] for C 36.3%, H 6.1%. 31P-{1H} NMR: Solution ([2H6] benzene) d at 87.6 (s) and -9.4 (s), IR [nu](CO) 1879, 1848 cm-1.
b) The remaining solid from the reaction was redisolved in toluene (15 cm3) and the same amount of pentane was added to this solution. A crystalline orange compound was obtained when the reaction mixture was cooled down to -30[ring]C for 3 days. This compound was characterised as [Pd6(u-Br)4(u-CO)4(PBut3)4]. Elemental Analyses: found C 35.6%, H 5.4%, required for C38H80Br3O2P3Pd4.[C7H8] C 35.9%, H 6.0%. 31P-{1H} NMR: Solution ([2H6] acetone) d at 85.9 (s). IR [nu](CO) 1871 cm-1. FAB-MS (m/v)/assignment: [M-CO-Br]+, 1766, [M-CO-Br-PBut3]+, 1564, [M-3CO-3Br-PBut3]+, 1268, [M-3CO-4Br-PBut3]+, 1183.
[Pd4(u-Br)3(u-CO)2((But3)2PMe2CH2)(PBut3)2] from [Pd4(OAc)4(CO)4].2OAc
[Pd4(OAc)4(CO)4].2OAc (0.081 g, 0.09 mmol) was dissolved in toluene (25 cm3) with stirring. PBut3 (0.072 g, 0.36 mmol) was separately dissolved in toluene and added to the previous solution. Immediately after the addition, the initially yellow solution changed to a dark orange colour. After 15 minutes CBr4 (0.03 g, 0.09 mmol) was added to the solution. After 4 hrs the reaction mixture was filtered and hexane (25 cm3) added to it. The reaction mixture was kept at 4[ring]C during three days and a crystalline dark orange compound came out (0.066, 56% yield). Suitable crystals for a single-crystal X-Ray analysis were obtained from slow evaporation of a toluene/hexane mixture. Elemental Analyses: found C 36.7%, H 6.1%, required C38H80Br3O2P3Pd4.0.5[C7H8] for C 36.3%, H 6.1%. 31P-{1H} NMR: Solution ([2H6] benzene) d at 87.4 (s) and -9.4 (s), IR [nu](CO) 1880, 1848 cm-1. FAB-MS (m/v)/assignment: [M-CO]+, 1298, [M-2CO]+, 1270, [M-2CO-Br-Pd]+, 1084, [M-2CO-Br-2Pd-PBut3]+, 775, [M-2CO-2Br-2Pd-PBut3]+, 695, [M-2CO-2Br-2Pd-2PBut3]+, 413.
Reaction of [Pd2(u-I)2(PBut3)2] with CO
[Pd2(u-I)2(PBut3)2] (0.04 g, 0.05 mmol) was dissolved in an small amount of toluene (10 ml) and CO was bubbled through this solution for 10 min. A change of colour from purple to red-wine was observed. The reaction mixture was stirred under CO for one more hour. After this time ethanol (10 ml) was added and the reaction mixture was kept under CO at 4[ring]C for 48 hr. A dark purple solid precipitated and was formulated as [Pd6(u-CO)4(u-I)4(PBut3)4] (0.011 g, 31%). Elemental Analyses: found C 31.7%, H 5.0%, required for C52H108I4O4P4Pd6.0.5[C7H8] C 31.7%, H 5.3%. 31P-{1H} NMR: Solution ([2H6] benzene) d at 95.4 (s), IR (KBr) [nu](CO) 1889 and 1885 cm-1; solution IR (in toluene): 1896.2(vs) cm-1.
Reaction of [Pd2(u-Br)2(PBut3)2] with CNXyl
Four equivalents of CNXyl (0.045 g, 0.34 mmol) in acetone (15 cm3) were added to a solution of [Pd2(u-Br)2(PBut3)2] (0.066 g, 0.084 mmol) in toluene (15 cm3). After the addition an immediate change in colour from dark green to dark orange was observed. The reaction was left to stand for 2 hrs. After this time hexane was added (40 cm3) and a dark yellow crystalline solid precipitated of [Pd2(Br)2(CNXyl)4] (0.056g, 75%). Elemental Analyses: found C 48.3%, H 3.8%, N 6.1% required for C36H36N4Br2Pd2 C 48.2%, H 4.0%, N 6.2%. 1H NMR: Solution ([2H6] benzene) d at 6.6 (t), 6.5 (d) and 2.3 (s) 3J(HH) 8Hz . IR [nu](CN) 2154 cm-1. FAB-MS (m/v)/assignment: [M]+, 896, [M-Br]+, 819, [M-Br-CNXyl]+, 688, [M-Br-CNXyl-Pd]+, 580, [M-Br-2CNXyl-Pd]+, 449, [M-2Br-2CNXyl-Pd]+, 368, [M-2Br-3CNXyl-Pd]+, 236.
Reaction of [Pd2(u-I)2(PBut3)2] with CNXyl
This was prepared by the same method than [Pd2(Br)2(CNXyl)4] using [Pd2(u-I)2(PBut3)2] (0.06 g, 0.07 mmol) and CNXyl (0.4 g, 0.27 mmol). Recrystallised from toluene/hexane at -30[ring]C (0.04 g, 57.1 %). Elemental Analyses: found C 43.6%, H 4.2%, N 4.7% required for C36H36N4I2Pd2 C 43.6%, H 3.6%, N 5.7%. IR [nu](CN) 2108, 2151 cm-1. FAB-MS (m/v)/assignment: [M-I]+, 862, [M-I-CNXyl]+, 731, [M-I-CNXyl-Pd]+, 625, [M-I-3CNXyl-Pd]+, 438, [M-2I-3CNXyl-Pd]+, 236.
Reaction of [Pd2(u-Br)2(PBut3)2] with H2:
[Pd2(u-Br)2(PBut3)2] (0.08g, 0.10 mmol) was dissolved in toluene and H2 was bubbled through the solution for 10 min. The reaction was stirred under H2 for further 4 hrs. After this time the reaction mixture was filtered (to separate the product from the palladium black) and the solvent removed. A colourless white solid was obtained after recrystallising the crude product from hexane that was formulated as trans-[PdBrH(PBut3)2]. Elemental analyses: found 31P-{1H} NMR: Solution ([2H6] benzene) d at 84.0 ppm (s), 1H- NMR: Solution ([2H6] benzene) d at -15.5 ppm (t) (2J(P-H) 7 Hz)