Preparation, Structure, and Reactivity of Dipalladium(I) Complexes Containing the Carbanion 2-C₆F₄PPh₂: Coexistence of Distinct, Noninterconverting Head-to-Head [Dipalladium(0/II)] and Head-to-Tail [Dipalladium(I)] Species

Abstract

Comproportionation of trans-[Pd(κ 2-2-C 6 F 4 PPh 2) 2 ] with [PdL 4 ] (L = PPh 3 , AsPh 3) gives metal− metal-bonded dipalladium(I) complexes [Pd 2 I (μ-2-C 6 F 4 PPh 2) 2 (L) 2 ] [L = PPh 3 (5), AsPh 3 (6)] in which the bridging ligands adopt a head-to-tail arrangement. The corresponding diplatinum(I) complex [Pt 2 I (μ-2-C 6 F 4 PPh 2) 2 (PPh 3) 2 ] (9) is obtained similarly from [Pt(κ 2-2-C 6 F 4 PPh 2) 2 ] and [Pt(PPh 3) 3 ]. The separations between the metal atoms in the dipalladium(I) complexes [2.5740(3) Å (5), 2.5511(3) Å (6)] are slightly less than that in the diplatinum(I) complex 9 [2.61179(15) Å]. The axial triphenylarsine ligands of 6 are replaced by tert-butyl isocyanide to give the dipalladium(I) complex [Pd 2 I (μ-2-C 6 F 4 PPh 2) 2 (CN t Bu) 2 ] (7). However, treatment of trans-[Pd(κ 2-2-C 6 F 4 PPh 2) 2 ] with [Pd(CN t Bu) 2 ], generated in situ from a mixture of tert-butyl isocyanide and [Pd(η 5-Cp)(η 3-allyl)], gives a formally mixed-valent palladium(0)−palladium(II) complex [Pd 2 0/II (μ-2-C 6 F 4 PPh 2) 2 (CN t Bu) 2 ] (8), in which the bridging ligands are arranged head-to-head. In contrast, comproportionation of [Pt(κ 2-2-C 6 F 4 PPh 2) 2 ] with [Pt 3 (CN t Bu) 6 ] gives the diplatinum(I) complex [Pt 2 I (μ-2-C 6 F 4 PPh 2) 2 (CN t Bu) 2 ] (10) analogous to 7; there was no evidence for the formation of a dinuclear mixed-valent species. Although complexes 7 and 8 are isomers, with similar Pd−Pd separations [2.5803(4) Å (7), 2.5580(2) Å (8)], they do not interconvert in solution. The diplatinum(I) complex 9 undergoes oxidative addition with iodine to give an A-frame cation, [Pt 2 (μ-I)(μ-2-C 6 F 4 PPh 2) 2 (PPh 3) 2 ] + , isolated as its PF 6 − salt (11). In contrast, the dipalladium(I) complex 5 eliminates one of the PPh 3 ligands when it undergoes oxidative addition with halogens and with methyl iodide, the products being A-frame dipalladium(II) complexes [Pd 2 X(μ-Y)(μ-2-C 6 F 4 PPh 2) 2 (PPh 3)] [X = Y = I (12), Cl (13); X = Me, Y = I (14)]. The metal−metal distances in 11−14 [2.9478(5) Å (11), 2.8078(7) Å (12), 2.8241(3) Å (13), and 2.8013(5) Å (14)] are ca. 0.3 Å greater than in their dimetal(I) precursors, consistent with a weaker metal−metal interaction in the dimetal(II) complexes. Unexpectedly, reaction of 5 with iodobenzene gives a mononuclear palladium(II) complex, cis-[Pd(κ 2 C,P-2-C 6 F 4 PPh 2)(κC-2-C 6 F 4 PPh 2)(PPh 3)] (15). This is suggested to be formed by a sequence of (a) oxidative addition of iodobenzene to 5 to give a σ-phenyl complex analogous to the σ-methyl complex 14, (b) a change in the binding mode of one of the 2-C 6 F 4 PPh 2 ligands from μto κ 2-, and (c) reductive elimination of tetraphenylphosphonium iodide and loss of Pd(0).

Insights into Functional‐Group‐Tolerant Polymerization Catalysis with Phosphine–Sulfonamide Palladium(II) Complexes

“…The Pd I Pd I distance of 2.544(1) Å in DIPP (1 + ‐SbF 6 ) decomp. is close to that in [Pd 2 (NPN‐NPN) 2 ](BF 4 ) 2 (2.5489(7) Å),16a but slightly shorter than those in [Pd I 2 (μ‐2‐C 6 F 4 PPh 2 ) 2 (L) 2 ] (L=PPh 3 , 2.5740(3) Å; L=AsPh 3 , 2.5511(3) Å; L= t BuNC, 2.5803(4) Å)16b and much shorter than that in [{(Ph 2 B(PPh 2 ) 2 )Pd} 2 ] (2.728(6) Å) 15…”

Formation of Heterobimetallic Complexes by Addition of d10-Metal Ions to cis-[(dppe)M(κC-2-C6F4PPh2)2] (M = Ni, Pd, and Pt)

“…The isomer ratio changed from 1:4 to 1:10 after 1 week and to 1:15 after 2 weeks, but no further change was observed. In an earlier example of head-to-head and head-to-tail isomerism of μ-2-C 6 F 4 PPh 2 , viz., [Pd 2 (μ-2-C 6 F 4 PPh 2 ) 2 ( tert -BuNC) 2 ], the isomers showed no evidence of interconversion …”

Novel Di- and Trinuclear Palladium Complexes Supported byN,N′-Diphosphanyl NHC Ligands andN,N′-Diphosphanylimidazolium Palladium, Gold, and Mixed-Metal Copper–Gold Complexes

“…The Pd–Pd distance [2.6574(5) Å] is in the typical range of Pd I –Pd I covalent bonds . The PC NHC P ligand coordination leading to a centrosymmetric palladium­(I)–palladium­(I) complex can be compared with the situation in dinuclear palladium complexes with metalated triphenylphosphine derivatives, but in the latter case, both the head-to-tail Pd I –Pd I and the head-to-head Pd 0 –Pd II isomers were isolated and found to be noninterconverting …”