Ruthenaphosphaalkenyls: Synthesis, Structures, and Their Conversion to η²-Phosphaalkene Complexes

η1:η2-P-Pyrazolylphosphaalkene Complexes of Ruthenium(0)

“…As we have previously described [29,40] Me2 ] each afford a single complex (3c-d respectively), which is spectroscopically comparable to those obtained similarly from 1a and 1b [29,30]. Thus, the characteristic resonances for the phosphaalkenyl and PPh3 ligands are lost, being replaced by three new, mutually coupling, resonances (1:1:1 ratio) in the region 50-30 ppm, which is commonly associated with saturated (λ 3 σ 3 ) phosphorus centers.…”

“…Thus, the characteristic resonances for the phosphaalkenyl and PPh3 ligands are lost, being replaced by three new, mutually coupling, resonances (1:1:1 ratio) in the region 50-30 ppm, which is commonly associated with saturated (λ 3 σ 3 ) phosphorus centers. In each case, the lower frequency resonance is identified as that associated with the phosphacarbon, on the basis of a 1 H-31 P-HMBC correlation to the, now appreciably shielded, "CH(SiMe2R)" moiety (identified from 1 H- 29 Si-HMBC spectra and a significant 1 JPC coupling (~70 Hz)). The latter is observed at δH ~1.7 and δC ~42, which, though appreciably lower frequency than for a classical alkenyl "CH", remains somewhat deshielded for a fully saturated "alkyl" moiety.…”

“…As we have previously described [29,40], substituents, or indeed those of the pyrazolyl moiety, resulting variations in the atom-specific parameters (e.g., NMR shielding effects) offering a potential means of quantification. In seeking to assess the influence of such factors, and thus potentially to elaborate means of control over reactivity, we report herein the synthesis and characterization of an extended range of these novel pyrazolylphosphaalkene complex.…”

“…Notwithstanding, we have additionally observed an unusual reaction to proceed when 1a or 1b is exposed the lithium pyrazolates Li[pz ] (pz = pz, pz Me2 , pz CF3 , pz Me,CF3 ), giving rise to the unprecedented phosphaalkene complexes [Ru{η 1 -N:η 2 -P,C-P(pz )=CH(SiMe 2 R)}(CO)(PPh 3 ) 2 ] (Scheme 1) [29,30], which feature an apparent 3-member (Ru-P-C) metallacyclic core, bridged by a pyrazolyl moiety. Also replicated using Hill's [Ru{P=CH( t Bu)}Cl(CO)(PPh 3 ) 2 ], this chemistry would perhaps imply ambiphilicty for the ruthenaphosphaalkenyl motif, if not directly of the alkenyl phosphorus center.…”

“…First described in 1985 [24], such systems remain relatively rare, though-with the exception of type E-all possible motifs have been realized, with P-metalla-(type A) and C-metalla-(type B) systems the most heavily studied. Recently, as part of an extended program investigating transition metal compounds featuring low-coordinate phosphacarbons with potential for conjugation [25][26][27][28], we have prepared and studied a range of ruthenaphosphaalkenyl complexes of the type [Ru{P=CH(SiMe2R)}Cl(CO)(PPh3)2] (R = Me 1a, Ph 1b, Tol 1c) [29,30]. These are prepared by hydroruthenation of phosphaalkynes R3SiC≡P, following from methodology developed initially by Hill and Jones for t BuC≡P and related systems [31][32][33], and superficially related to Nixon's independent reduction of [(Ph3P)2Pt(η 2 -P≡C t Bu)] with Schwartz's reagent [34].…”