An Unusal Case of Facile Non‐Degenerate PC Bond Making and Breaking

Abstract

Oxidation of Li/X phosphinidenoid complex 2, obtained via selective deprotonation from the P-H precursor 1, with [Ph(3)C]BF(4) led to the formation of two P-F substituted diorganophosphane complexes 6,7; the latter tautomer 7 formed via H-shift from 6. In contrast, oxidation of 2 with [(p-Tol)(3)C]BF(4) led to three major and one minor intermediates at low temperature, which we tentatively assign to two pairs of P-C atropisomers 10 a,a' and 10 c,c' and which differ by the relative orientations of their CH(SiMe(3))(2) and W(CO)(5) groups. Conversion of all isomers led finally to complex 11 having a ligand with a long P-C bond to the central trityl* carbon atom, firmly established by single-crystal X-ray analysis. DFT calculations at the B3LYP/def2-TZVPP//BP86/def2-TZVP level of theory on real molecular entities revealed the structures of the in situ formed combined singlet diradicals (4+5 and 5+9) and the nature of intermediates on the way to the final product, complex 11. Remarkable is that all isomers of 11 possess relative energies in the narrow energy regime of about 20 kcal mol(-1). A preliminary study revealed that complex 11 undergoes selective P-C bond cleavage at 75 °C in toluene solution.

P‐OR Functional Phosphanido and/or Li/OR Phosphinidenoid Complexes?

“…The molecular structure of P-methylphosphane complex 5a was confirmed by X-ray analysis ( Figure (2), P-W 2.5045 (7), P-C8 1.819(3), P-C1 1.814(3), O1-C2 1.398(3); C1-P-O1 100.28 (12), C1-P-C8 106.89 (13), C1-P-W 115.28(10), O1-P-C8 97.66 (12), O1-P-W 114.80(8), C8-P-W 119.05 (9), P-O1-C2 124.68 (17). P-Chlorophosphane complex 6 showed a resonance at δ = 186.7 ppm in the 31 P NMR spectrum with a large coupling constant ( 1 J W,P = 335.7 Hz).…”

“…[8b] The high negative charge density at the phosphorus atom also enabled redox reactions, as the initial studies revealed: SET oxidation occurs with tritylium salts, thus leading to transient P-X functional phosphanyl complexes that were detected by EPR spectroscopy. [12] Recently, we gained further insight into these systems. [12] Recently, we gained further insight into these systems.…”

“…The high negative charge density at the phosphorus atom also enabled redox reactions, as the initial studies revealed: SET oxidation occurs with tritylium salts, thus leading to transient P ‐X functional phosphanyl complexes that were detected by EPR spectroscopy 11. The latter not only possess high electron‐spin density at the phosphorus atom (70–85 %) but also underwent phosphorus‐centered reactions thereby providing new perspectives in synthesis11 as well as new insights into systems possessing very weak P–C bonds 12…”

First synthesis of chloroformylphosphane complexes

“…The knowledge about P III -functional chloroformylphosphanes is extremely scarce, e.g., P-silylated derivatives are known as intermediates in the preparation of phosphaketenes [5], and only two derivatives having a triphenylmethyl group bound to phosphorus [6] have been described as relatively stable compounds. We became attracted to this intriguing class of phosphorus compounds having a weak P-C bond [7], and are thus trying to evaluate the influence of transition-metal complex formation on stability of the species. Here, we describe the first syntheses of P-functional chloroformylphosphane complexes based on reactions of lithium/halogen phosphinidenoid tungsten(0) complexes with phosgene.…”

Selective phosphanyl complex trapping using TEMPO. Synthesis and reactivity of P-functional P-nitroxyl phosphane complexes

“…7 Recently, we have demonstrated that Li/Hal phosphinidenoid ligands (Hal = F, Cl) undergo one-electron oxidation with triarylcarbenium tetrafluoroborates to yield highly reactive P-functional phosphanyl tungsten(0) complexes of type I (R 1 = CH(SiMe 3 ) 2 , R 2 = Cl, F or R 1 = Cp*, R 2 = Cl) together with triarylmethyl radicals. 8,9 In the case of the P-Cl phosphanyl complexes 8 heterocoupling in para position of the trityl unit occurred. In the case of P-F derivative 9 even coupling at the central carbon atom of the triarylmethyl radical was possible, when tris( p-methylphenyl)methyl tetrafluoroborate was employed as an oxidant.…”