Combined QTAIM and ETS-NOCV investigation of the interactions in ClnM[PhB(NtBu)2] complexes with M = Si & Ge (n = 0), As & Sb (n = 1), Te & Po (n = 2)

In this work, the nature of the chemical interactions between the metalloid atom (M = Si, Ge, As, Sb, Te, Po) and the nitrogen atoms in the bora-amidinate (bam) complexes (Cl_nM[PhB(N^tBu)₂]) are investigated, mainly via density-based indices. The descriptors used are derived using the quantum theory of atoms in molecules and natural orbitals for chemical valence approaches. It is shown that the strongest interaction is achieved with silicon. Indeed, it is generally the lightest metalloid in a particular group of the periodic table (i.e., Si, As, and Te for groups 14-16, respectively) that exhibits the strongest bond in the bam complex. This suggests that the atomic radius of the metalloid is a useful parameter for predicting the bonding strength. Extended transition state (ETS) decomposition results indicate that the interactions are more electrostatic than due to orbital interactions.

New Bonding Modes for Boraamidinate Ligands in Heavy Group 15 Complexes: Fluxional Behavior of the 1:2 Complexes, LiM[PhB(NtBu)2]2 (M = As, Sb, Bi)

The reactions of MCl3 with Li2[PhB(NtBu)2] in 1:1, 1:1.5, and 1:2 molar ratios in diethyl ether produced the monoboraamidinates ClM[PhB(NtBu)2] (1a, M = As; 1b, M = Sb; 1c, M = Bi), the novel 2:3 boraamidinate complexes [PhB(NtBu)2]M-micro-N(tBu)B(Ph)N(tBu)M[PhB(NtBu)2] (2b, M = Sb; 2c, M = Bi), and the bisboraamidinates LiM[PhB(NtBu)2]2 (3a, 3a.OEt2, M = As; 3b, M = Sb; 3c.OEt2, M = Bi), respectively. The 2:3 complexes 2b and 2c were also observed in the reactions carried out in a 1:2 molar ratio at room temperature. All complexes have been characterized by multinuclear NMR spectroscopy (1H, 7Li, 11B, and 13C) and by single-crystal X-ray structural determinations. The molecular units of the mono-boraamidinates 1a-c are isostructural, but their crystal packing is distinct as a result of stronger intermolecular close contacts going from 1a to 1c. In the novel 2:3 bam complexes 2b and 2c, each metal center is N,N'-chelated by a bam ligand and these two [M(bam)]+ units are bridged by the third [bam]2- ligand. The structures of the unsolvated bis-boraaminidate complexes 3a and 3b consist of [Li(bam)]- and [M(bam)]+ monomeric units linked by Li-N and M-N bonds to give a tricyclic structure. Solvation of the Li+ ion by diethyl ether results in a bicyclic structure composed of four-membered BN2As and six-membered BN3AsLi rings in 3a.OEt2. In contrast, the analogous bismuth complex 3c.OEt2 exhibits a tetracyclic structure. Variable-temperature NMR studies reveal that the nature of the fluxional behavior of 3a-c in solution is dependent on the group 15 center.

Syntheses and Structures of Magnesium and Zinc Boraamidinates: EPR and DFT Investigations of Li, Mg, Zn, B, and In Complexes of the [PhB(NtBu)2]•- Anion Radical

The first magnesium and zinc boraamidinate (bam) complexes have been synthesized via metathetical reactions between dilithio bams and Grignard reagents or MCl2 (M = Mg, Zn). The following new classes of bam complexes have been structurally characterized: heterobimetallic spirocycles {(L)mu-Li[PhB(mu-NtBu)2]}2M (6a,b, M = Mg, L = Et2O, THF; 6c, M = Zn, L = Et(2)O); bis(organomagnesium) complexes {[PhB(mu3-NtBu)2](MgtBu)2(mu3-Cl)Li(OEt2)3} (8) and {[PhB(mu3-NtBu)2](MgR)2(THF)2} (9a, R = iPr; 9b, R = Ph); mononuclear complex {[PhB(mu-NDipp)2]Mg(OEt2)2} (10). Oxidation of 6a or 6c with iodine produces persistent pink (16a, M = Mg) or purple (16b, M = Zn) neutral radicals {Lx-mu-Li[PhB(mu-NtBu)2]2M}. (L = solvent molecule), which are shown by EPR spectra supported by DFT calculations to be Cs-symmetric species with spin density localized on one of the bam ligands. In contrast, characterization of the intensely colored neutral radicals {[PhB(mu-NtBu)2]2M}. (5c, M = In, dark green; 5d, M = B, dark purple) reveals that the spin density is equally delocalized over all four nitrogen atoms in these D2d-symmetric spirocyclic systems. Oxidation of the dimeric dilithio complex {Li2[PhB(mu4-NtBu)2]}2 with iodine produces the monomeric neutral radical {[PhB(mu-NtBu)2]Li(OEt2)x}. (17), characterized by EPR spectra and DFT calculations. These findings establish that the bam anionic radical [PhB(NtBu)2].- can be stabilized by coordination to a variety of early main-group metal centers to give neutral radicals whose relative stabilities are compared and discussed.

Syntheses and X-ray structures of monocyclic, bicyclic, and spirocyclic gallium and indium boraamidinates

The reactions of [Li(2)[PhB(N(t)Bu)(2)]](2) with GaCl(3) in various stoichiometries yield [Li(thf)(4)][PhB(mu-N(t)Bu)(2)GaCl(2) x GaCl(3)] (1), [PhB(mu-N(t)Bu)(2)GaCl](2) (2), and [mu-Li(OEt(2))[PhB(N(t)Bu)(2)]Ga] (3a), a series of complexes in which the three chloride ligands are successively replaced by the dianion [PhB(N(t)Bu)(2)](2-). The X-ray structures of 1, 2, and 3a show that the boraamidinate ligand adopts an N,N'-chelating mode. In the ion-separated complex 1, one of the nitrogen atoms is coordinated to a GaCl(3) molecule. The related indium complexes [mu-LiCl(thf)(2)][PhB(mu-N(t)Bu)(2)InCl](2) (4) and [mu-Li(OEt(2))[PhB(mu-N(t)Bu)(2)]In] (3b) were obtained in a similar manner. Complex 4 is the indium analogue of 2 with the incorporation of a bissolvated LiCl molecule. In 3a and 3b the spirocyclic [[PhB(mu-N(t)Bu)(2)](2)M](-) (M = Ga, In) anions are N,N'-chelated to the [Li(OEt(2))](+) counterion. Prolonged reactions result in the formation of [PhB(mu-N(t)Bu)(2)GaCl][(t)BuN(H)GaCl(2)] (5) and [[PhB(mu-N(t)Bu)(2)InCl][(t)BuN(H)InCl(2)][mu-LiCl(OEt(2))(2)]] (6), respectively. The X-ray structures of 5 and 6 reveal bicyclic structures which formally involve the entrapment of the monomers (t)BuN(H)MCl(2) by a four-membered BN(2)M ring (M = Ga, In). The synthesis and X-ray structure of Cl(2)Ga[mu-N(H)(t)Bu](2)GaCl(2) are also reported.

Syntheses and X-ray structures of boraamidinate complexes of lithium, phosphorus, and tellurium

The dilithiated boraamidinate complexes {Li2[RB(N-t-Bu)2]}2 (1a, R = Ph; 1b, R = t-Bu), prepared by the reaction of B[N(H)-t-Bu]3 with three equivalents of LiR, are shown by X-ray crystallography to have dimeric structures consisting of a distorted Li4N4 cube capped on two opposite faces by RB units. Reactions of 1a with TeCl4 or PX3 (X = Cl, Br) yielded complexes PhB(μ-N-t-Bu)2TeCl2 (2) and PhB(μ-N-t-Bu)2PX (4a, X = Cl; 4b, X = Br), respectively. The structures of 2 and 4b were determined by X-ray crystallography. In the solid state, complex 2 forms a dimer with weak Te···Cl contacts (3.2411(6) Å). Complex 4b is monomeric with a P—Br bond length of 2.3047(11) Å. The reactions of 2 and 4a with the appropriate amounts of Li[N(H)-t-Bu] produce the monomeric tellurium imide PhB(μ-N-t-Bu)2Te=N-t-Bu and the amido derivative PhB(μ-N-t-Bu)2PN(H)-t-Bu (4c), respectively. The X-ray structure of 4c was determined. Deprotonation of 4c with n-BuLi produces the dimeric monolithium derivative {Li[PhB(μ-N-t-Bu)2PN-t-Bu]}2 (5), which was shown by X-ray crystallography to have a centrosymmetric structure with a central transoid Li2N2 ring.Key words: boraamidinates, lithium, tellurium, phosphorus, X-ray structures.