Facile Addition of B–H and B–B Bonds to an Iron(IV) Nitride Complex

Abstract

The nitride ligand in the iron(IV) complex PhB( i Pr2Im)3FeN reacts with boron hydrides to afford PhB( i Pr2Im)3FeN(B)H (B = 9-BBN (1), Bpin (2)) and with (Bpin)2 to afford PhB( i Pr2Im)3FeN(Bpin)2 (3). The iron(II) borylamido products have all been structurally and spectroscopically characterized, demonstrating facile insertion into B–H and B–B bonds by PhB( i Pr2Im)3FeN. Density functional theory (DFT) calculations reveal that the quintet state (S = 2) is significantly lower in energy than the singlet (S = 0) and triplet (S = 1) states for all products. Stoichiometric reaction with (Bpin)2 does not produce the mono-borylated iron imido species PhB( i Pr2Im)3FeN(Bpin). DFT calculations suggest that this is because PhB( i Pr2Im)3FeN(Bpin) is unstable toward disproportionation to the starting iron(IV) nitride and PhB( i Pr2Im)3FeN(Bpin)2. Attempts at B–C bond insertion using phenyl- and benzyl-pinacol borane were unsuccessful, which we attribute to unfavorable kinetics.

A S=3/2 Cr(III) Complex In A Square‐Capping NHC Framework

“…Ph and P 2 Me PP 2 Ph frameworks consisting of five phosphine donors. [7] While the coordination chemistries of monodentate, [8][9][10] bidentate, [11][12][13][14][15][16] tripodal [17][18][19][20] and macrocyclic [21][22][23][24][25] NHC ligands are well developed, study of the coordination chemistry of square-capping NHC frameworks are in their infancy. NHC ligands are an attractive alternative to widely used phosphine ligands as they share strong σ-donor and moderate π-accepting ability, are insensitive to oxidizing conditions, [26] and can support a wide variety of oxidation states best exemplified by isolable complexes of iron ranging from + 6 to 0.…”

“…This ligand is most closely related to the dianionic NN 4 topology of the B 2 Pz 4 Py ligand, [1,2] as well as to charge neutral frameworks consisting of five nitrogenous donors like N4Py, [3] ImPy 3 N, [4] PY5Me 2 and their derivatives; [5,6] or the charge neutral P 2 Ph PP 2 Ph and P 2 Me PP 2 Ph frameworks consisting of five phosphine donors [7] . While the coordination chemistries of monodentate, [8–10] bidentate, [11–16] tripodal [17–20] and macrocyclic [21–25] NHC ligands are well developed, study of the coordination chemistry of square‐capping NHC frameworks are in their infancy. NHC ligands are an attractive alternative to widely used phosphine ligands as they share strong σ‐donor and moderate π‐accepting ability, are insensitive to oxidizing conditions, [26] and can support a wide variety of oxidation states best exemplified by isolable complexes of iron ranging from +6 to 0 [13,19,27] …”

A Tetrapodal Penta‐Carbene Ligand and Iron(III) Complex

“…Coordination compounds of the B 2 Pz 4 Py ligand have provided complexes of Fe and Co relevant to nitrogen fixation, [25][26][27] vitamin B12, [28] and dioxygen reduction. [29] Considering the rich chemistry of coordination complexes supported by monodentate, [30][31][32] bidentate, [33][34][35][36][37][38] tripodal [39][40][41][42] and macrocyclic [43][44][45][46][47] ligands consisting of N-heterocyclic carbene (NHC) donors a particularly striking absence in the tetrapodal pentadentate family of ligands are those composed of equatorial and axial NHC donor groups. Intrigued by the impact a pentadentate framework composed entirely of NHC donors would have on the chemistry of first-row transition metals we undertook the preparation of the tricationic protoligand [CC 4H5 Me ](OTf) 3 (3).…”

Mechanism of Nitrogen Reduction to Ammonia in a Diiron Model of Nitrogenase

“…As there is still no consensus catalytic cycle for nitrogenase and specific details on the individual steps remain controversial, many groups have created biomimetic complexes of the active site of nitrogenase. In particular, biomimetic complexes have been created of metalloenzymes, which generally take a transition metal with a first-coordination sphere analogous to the enzyme and investigate its structure, electronic properties, and reactivity patterns in solution. – Many of those studies investigated mononuclear metal–nitrido and metal–imido complexes and their functional properties. – In more recent years also biomimetic nitrogenase complexes with diiron centers have been synthesized and investigated. – …”

“… 12 – 23 Many of those studies investigated mononuclear metal–nitrido and metal–imido complexes and their functional properties. 24 – 37 In more recent years also biomimetic nitrogenase complexes with diiron centers have been synthesized and investigated. 38 – 46 …”