Phosphaazaallene Dimerization and Phosphaallene Isomerization:  Catalysis by Zerovalent Palladium and Platinum Complexes

Abstract

Several Pd(0) complexes catalyze the dimerization of Mes*PCNPh [2, Mes* = 2,4,6-(t-Bu)3C6H2] to the unsymmetrical heterocycle Mes*P(μ-CNPh)NPh(μ-CPMes*) (5). The symmetrical dimer [Mes*P(μ-CNPh)]2 (7), which forms slowly by uncatalyzed dimerization of 2, does not interconvert with 5; both 5 and 7 were structurally characterized by X-ray crystallography. The Pt complexes PtL2[η2-(P,C)-Mes*PCNPh] [8, L = 1/2 dppe (Ph2PCH2CH2PPh2); 9, L = PPh3; 10, L = PCy3 (Cy = c-C6H11)], models for intermediates in the catalysis, were prepared. Isomerization of Mes*PCCPh2 (3) to the phosphaindan [2,4-(t-Bu)2C6H2(6-CMe2CH2PCHCPh2)] (6), which we previously observed with Rh(I) catalysts, is catalyzed by Pt(PCy3)2 or the known Pt(PPh3)2[η2-(P,C)-Mes*PCCPh2] (12). Comparison of the metal-mediated reactions of 2 and 3 suggests that the initial steps in the catalyses, coordination of the phosphacumulene to M(0), followed by loss of a ligand, are similar.

Fragmentation of an N-Substituted One-Coordinate Phosphorus (Phosphaalkyne): Plausible Generation of Monovalent Phosphorus Species

“…The two downfield signals correspond to the four-membered-ring phosphorus atoms. Similar patterns in the 31 P NMR spectra of analogous 2,4-diimino-1,3-diphosphetanes have been described …”

Heavy Allenes and Cumulenes ECE‘ and ECCE‘ (E = P, As, Si, Ge, Sn; E‘ = C, N, P, As, O, S)

“…An η 2 -coordination was also observed between 1 and platinum complexes. 80,81 With phosphaallene 1 and some rhodium complexes, a quantitative isomerization to the phosphaindane 69 was observed 81,82 By studying group 6 metal carbonyl complexes of -PdP-, -PdC<, -PdCdC<, and -PdCdP-, Yoshifuji found that their 31 P chemical shifts correlate to one another so that their structures in solution could be determined. 83…”

“…85,86 (Ph 3 P) 4 Pd catalyzes the dimerization of ArPdCd NPh but give another type of dimer involving a PdC and a CdN double bond. 81 100 can be characterized in 31 P NMR by an AX system at δ: 111 (ArPdC) and 32 ppm (ArP) with a coupling constant 2 J PP of 124 Hz. 81 We should note that it is rather unusual to find a compound such as 82 which exists in three isolable different forms, a monomer and two types of dimers.…”

On 1,3-phosphaazaallenes and their diverse reactivity

“…2,7 Even Mes*PCNPh slowly dimerizes in solution, whereas in the presence of catalytic amounts of Pd(PPh 3 ) 4 the unsymmetric fourmembered heterocycle is obtained. 8 Derivatives with a bulky cyclopropen-1-yl substituent at the phosphorus were synthesized by Regitz et al 9 In 1991 Grobe and co-workers demonstrated that the metastable (F 3 C)PCNtBu (can be handled at À40 C) is feasible by reacting the phosphaalkene precursor (F 3 C)P]CF 2 with three equivalents of H 2 NtBu. 10 Instead of dimerizing at higher temperatures, (F 3 C)PCNtBu decomposes to give uorinated cyclophosphanes (PCF 3 ) n and the isocyanide CNtBu.…”

“… 2,7 Even Mes*PCNPh slowly dimerizes in solution, whereas in the presence of catalytic amounts of Pd(PPh 3 ) 4 the unsymmetric four-membered heterocycle is obtained. 8 Derivatives with a bulky cyclopropen-1-yl substituent at the phosphorus were synthesized by Regitz et al 9 …”