Mixed donor-functionalised phosphinomethanide complexes of the alkali metals; synthesis, structures, and solution dynamics

Abstract

The mixed donor tertiary phosphine {(Me(3)Si)(2)CH}P(C(6)H(4)-2-CH(2)NMe(2))(C(6)H(4)-2-CH(2)OMe) (11) is accessible via the stepwise addition of [Li(C(6)H(4)-2-CH(2)NMe(2))] followed by [Li(C(6)H(4)-2-CH(2)OMe)] to the dichlorophosphine {(Me(3)Si)(2)CH}PCl(2). Phosphine 11 is readily deprotonated by Bu(n)Li to give the lithium phosphinomethanide [[{(Me(3)Si)(2)C}P(C(6)H(4)-2-CH(2)NMe(2))(C(6)H(4)-2-CH(2)OMe)]Li] (15), which undergoes metathesis reactions with the alkoxides MOBu(t) [M = Na, K] to give the heavier alkali metal phosphinomethanides [[{(Me(3)Si)(2)C}P(C(6)H(4)-2-CH(2)NMe(2))(C(6)H(4)-2-CH(2)OMe)]M(L)(n)](x) in good yield [M = Na (12), (L)(n) = Et(2)O, x = 1; M = K (13), n = 0, x = 2]. Compounds 12 and 13 adopt monomeric and dimeric structures, respectively, in the solid state. Variable-temperature NMR studies indicate that compounds 12 and 13 are highly fluxional in solution; this fluxionality arises from a dynamic equilibrium between two conformers, which differ in the orientation of the aromatic rings of the ligand. The nature of these conformers and their relative energies have been probed by DFT calculations, which show the two principal conformers to differ in energy by just 1.6 kcal mol(-1). Calculation of the (1)H NMR shielding tensors using the GIAO method reveals that the low field chemical shifts of one benzylic and one aromatic proton in the ground state conformer are due to their close proximity to the carbanion centre.

Facile One-Step Synthesis of MPHMes from MesPCl2 (M = Li, Na, K; Mes = 2,4,6-Me3C6H2)

“…Na–P distances [286.4(5) and 284.6(5) pm] are comparable to those found in other structurally characterized sodium phosphanides, e.g., [Na(thf) 2 (PMes)(SiF t Bu 2 )] (289.0(1) pm) and [Na(pmdeta)(μ-PHCy)] 2 (291.0(8) pm) . The coordination sphere of sodium is completed by two nitrogen atoms from a bidentate TMEDA ligand, and an unusual coordination number of four is achieved by each sodium atom. , The average Na–N distance of 246.6(1) pm is slightly shorter than the values of 254.0(2) pm in [Na(pmdeta)(μ-PHCy)] 2 and 265.6(3) pm in [Na(pmdeta)(μ-Ph)] 2 , Table .…”

Applications of nuclear shielding

“…Synthesised compounds [[R 2 C:P(C 6 H 4 -2-CH 2 NMe 2 -kN)(C 6 H 4 -2-CH 2 OMe-kO)-kP]M(L)n] x [R = Me 3 Si, (M = Na, Ln = Et 2 O, x = 1) or (M = K, n = 0, x = 2)] were studied by variable-temperature NMR and DFT calculations. 24 The GIAO method calculation of the 1 H NMR shielding tensors revealed that the low field chemical shifts of one benzylic and one aromatic proton in the ground state conformer are due to their close proximity to the carbanion centre. An automated fragmentation quantum mechanics/molecular mechanics (AF-QM/MM) approach developed to calculate ab initio protein NMR chemical shielding constants shows good agreement with standard SCF calculations of the NMR chemical shieldings for the mini-protein Trp cage.…”

From Stable PH‐Ylides to α‐Carbanionic Phosphines as Ligands for Zwitterionic Catalysts

“…In contrast, P1 in 4 a-Ph binds to the metal center, which thus represents a rare example of a sodium monophosphine complex. [16] The impact of introducing a negative charge in the αposition to the phosphorus atom on the phosphine nucleophilicity was first studied by computational methods. [17] Interestingly, natural bond orbital (NBO) analyses [18] on the phosphinomethanides 4-R in comparison phosphines 3-R showed no increase of negative charge at the phosphorus center.…”