1,1′-Bifunctional Aminophosphane Complexes via N–H Bond Insertions of a Li/Cl Phosphinidenoid Complex and First Studies on N/P Mono Functionalizations

Abstract

Syntheses of 1,1′-bifunctional aminophosphane complexes 3–10 was achieved by reacting Li/Cl phosphinidenoid complex 2 (R = CPh3) with secondary (Me2NH, Et2NH, Bn2NH, pyrrolidine, and piperidine), primary amines (EtNH2 and allyl amine), and ammonia. Furthermore, regioselective N-silylation of 11 (R = Me) was achieved using MeLi and Me3SiCl to give complex 12. In contrast, treatment of complex 6 with KHMDS in the presence of 18-crown-6 yielded K/NMe2 phosphinidenoid complex 13 subsequently reacted with MeI to give P–Me substituted 14. Complex 5 was deprotonated with KHMDS in the presence of 18-crown-6 and reacted with [Ph3C]­BF4 to yield complex 17 via single-electron transfer reaction and P,C-heterocoupling. Finally, selective P–N bond cleavage was achieved by treating complex 18 (R = t-Bu) with HCl­(g) to afford chlorophosphane complex 19.

Regioselective N- versus P-Deprotonation of Aminophosphane Tungsten(0) Complexes

“…Two substituents at the nitrogen centre shift the resonance to the downfield region. The observed 1 J W,P and 1 J P,H coupling constants of 3a-f are of similar magnitude, as expected from related derivatives [12,13,[15][16][17].…”

“…In comparison to, e.g., the CPh 3 -substituent, the tert-butyl substituent exerts a reduced steric shielding onto the phosphorus centre according to Tolman's cone angle concept [20]. This makes this finding particularly astonishing, as a lesser steric shielding onto the phosphorus centre should allow for these reactions to happen, especially as the same reactions had proceeded selectively for the P-CPh 3 substituted analogue of complex 2 [16].…”

“…The 31 P NMR resonance signals of complexes 3a-f were observed in the range of 37 to 91 ppm and are highfield-shifted compared to the starting material 1. The analogous P-CPh 3 substituted complexes are 5-10 ppm highfield-shifted [15,16], indicating that the tert-butyl substituent leads to a slightly lower shielding of the P nucleus. Two substituents at the nitrogen centre shift the resonance to the downfield region.…”

“…The alternative use of Li/Cl phosphinidenoid complexes in the formation of aminophosphane complexes of type IV was first reported by us in 2012, using the formal N-H insertion [12,13]. The broader scope of this E-H insertion chemistry was reported more recently [14][15][16][17] including an overview of formal N-H insertion of Li/X phosphinidenoid complexes [18], adding first examples of V, but focusing on sterically demanding substituents, such as triphenylmethyl and bis(trimethylsilyl)methyl, together with W(CO) 5 and Fe(CO) 4 metal fragments [12][13][14][15][16][17][18][19]. Studies on the chemistry of 1,1 -bifunctional aminophosphane complexes V included reactions targeting the P-N bond with hydrogen halides [7] and the P-H bond via deprotonation [12][13][14][15][16][17][18].…”

“…The latter has resulted in new M/NR' 2 phosphinidenoid complexes if the P-H deprotonation takes place. In contrast, the new 1,2-bifunctionality, i.e., the presence of a P-H and N-H bond, has allowed for initial investigations concerning N-functionalization and/or P/N bifunctional nucleophilicity, thus enabling to form threemembered P-heterocyclic ligands, if sterically demanding P-substituents were used [16].…”