Access to 1,1′‐Bifunctional Phosphane Iron(0) Complexes via P–N Bond‐Forming Reactions and Selective P‐Functionalizations

Abstract

Reaction of Li/Cl phosphinidenoid Fe(CO) 4 complex 2 with ammonia and different amines R 1 ,R 2 NH yielded complexes 3-5 (3: R 1 = R 2 = H; 4a: R 1 = H, R 2 = Me; 4b: R 1 = H, R 2 = iPr; 4c: R 1 = H, R 2 = tBu; 4d: R 1 = H, R 2 = allyl; 4e: R 1 = H, R 2 = Ph; 5: R 1 = Me, R 2 = Me) having 1,1′-bifunctional phosphane ligands via formal N-H bond insertion of the phosphorus center. Studies on deprotonation enabled access to the first struc- [a]

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

“…The 31 P resonance signals of M-5b are 20 ppm downfield-shifted in comparison to 3b, in general, which is in accordance to previously observed M/N(H)R phosphinidenoid complexes [15][16][17]. In addition, the 1 J W,P coupling constant has a characteristically small value [12][13][14][15][16][17][18][19].…”

“…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].…”

“…Therefore, the quest of regioselective deprotonation of 1,2-bifunctional aminophosphane complexes 3a-f emerged. Previous deprotonation studies of the related, but sterically more demanding, 1,2-bifunctional complexes have shown that one equivalent of base is sufficient, in the presence of a crown ether, to achieve full conversion to the M/N(H)R' phosphinidenoid complex [12,13,[15][16][17]. To study the system in hand, the following three bases were tested with respect to the deprotonation of 3a-c: KHMDS, which was used before [15][16][17], MeLi and n-BuLi, varying in basicity and nature of the counter ion.…”

“…Previous deprotonation studies of the related, but sterically more demanding, 1,2-bifunctional complexes have shown that one equivalent of base is sufficient, in the presence of a crown ether, to achieve full conversion to the M/N(H)R' phosphinidenoid complex [12,13,[15][16][17]. To study the system in hand, the following three bases were tested with respect to the deprotonation of 3a-c: KHMDS, which was used before [15][16][17], MeLi and n-BuLi, varying in basicity and nature of the counter ion. In particular, the Li cation can be expected to display stronger P-Li and/or N-Li interactions, compared to interactions with the significantly larger K cation.…”

“…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].…”