1.10 – Polypyrazolylborate and Scorpionate Ligands

A series of hydrotris(indazolyl)borates containing diverse substituents on the indazole ring and representing two types of regiochemistries have been synthesized. Indazoles with a 7-alkyl substituent or a 6,7-fused benzo ring formed ligands with boron bonded to the less hindered N-2 (=Tp3Bo), while those with alkyl or aryl substituents in any other position yielded ligands with boron bonded to the more hindered N-1 (=Tp4Bo), thus being the first example of homoscorpionates with 4,5-substituents. Octahedral homo- and heteroleptic complexes of Co, Fe, and Zn have been prepared and characterized, as well as complexes of the types [M(L)(NCS)], [Mo(L)(CO)2(η3-CH2CMeCH2)], [Rh(L)(COD)], and [Rh(L)(CO)2]. X-ray crystallography provided structures of the complexes [Rh(HB{3-methylindazol-1-yl}3)(COD)], 1 (space group P21/n; a = 11.766(2), b = 16.189(2), c = 15.149(2) A; β = 92.51(1)°; Z = 4; R = 0.0306 for 4318 independent reflections), [Co(HB{7-methylinazol-2-yl}3)(HB{3-neopentylpyrazol-1-yl}3)], 2 (space group P...

Hydrotris(indazolyl)borates: Homoscorpionates with Tunable Regiochemistry

Experimental and ab initio molecular orbital techniques are developed for study of aluminum species with large quadrupole coupling constants to test structural models for methylaluminoxanes (MAO). The techniques are applied to nitrogen- and oxygen-containing complexes of aluminum and to solid MAO isolated from active commercial MAO preparations. (Aminato)- and (propanolato)aluminum clusters with 3-, 4-, and 6-coordinate aluminum sites are studied with three (27)Al NMR techniques optimized for large (27)Al quadrupole coupling constants: field-swept, frequency-stepped, and high-field MAS NMR. Four-membered (aminato)aluminum complexes with AlN(4) coordination yield slightly smaller C(q) values than similar AlN(2)C(2) sites: 12.2 vs 15.8 MHz. Planar 3-coordinate AlN(2)C sites have the largest C(q) values, 37 MHz. In all cases, molecular orbital calculations of the electric field gradient tensors yields C(q) and eta values that match with experiment, even for a large hexameric (aminato)aluminum cage. A D(3d) symmetry hexaaluminum oxane cluster, postulated as a model for MAO, yields a calculated C(q) of -23.7 MHz, eta = 0.7474, and predicts a spectrum that is too broad to match the field-swept NMR of methylaluminoxane, which shows at least three sites, all with C(q) values greater than 15 MHz but less than 21 MHz. Thus, the proposed hexaaluminum cluster, with its strained four-membered rings, is not a major component of MAO. However, calculations for dimers of the cage complex, either edge-bridged or face-bridged, show a much closer match to experiment. Also, MAO preparations differ, with a gel form of MAO having significantly larger (27)Al C(q) values than a nongel form, a conclusion reached on the basis of (27)Al NMR line widths in field-swept NMR spectra acquired from 13 to 24 T.

Structural characterization of MAO and related aluminum complexes. 1. Solid-state (27)Al NMR with comparison to EFG tensors from ab initio molecular orbital calculations.

Reaction of LnI2 (Ln = Sm, Yb) with two equivalents of NaTpMe2 or reduction of Eu(TpMe2)2OTf gives good yields of the highly insoluble homoleptic Ln(II) complexes, Ln(TpMe2)2 (Ln = Sm (1a), Yb (2a), Eu (3a)). Use of the additionally 4-ethyl substituted TpMe2,4Et ligand produces the analogous, but soluble Ln(TpMe2,4Et)2 (1−3b) complexes. Soluble compounds are also obtained with the TpPh and TpTn ligands (Tn = thienyl), Ln(TpPh)2 (Ln = Sm, 1c; Yb, 2c) and Ln(TpTn)2 (Ln = Sm, 1d; Yb, 2d). To provide benchmark parameters for structural comparison the series of Sm(TpMe2)2X complexes (X = F, 1e; Cl, 1f; Br, 1g; I, 1h; BPh4, 1j) were prepared either via oxidation of the Sm(TpMe2)2 or salt metathesis from SmX3 (X = Cl, Br, I). The solid-state structures of 1−3a, 1b, 1−2c and 1e, 1f, 1h, and 1j were determined by single-crystal X-ray diffraction. The homoleptic bis-Tp complexes are all six-coordinate with trigonal antiprismatic geometries, planes of the κ3-Tp ligands are parallel to one another. In the series of S...

Synthesis and Structural Comparison of a Series of Divalent Ln(TpR,R‘)2 (Ln = Sm, Eu, Yb) and Trivalent Sm(TpMe2)2X (X = F, Cl, I, BPh4) Complexes

Adducts of the ligand bis(1,2,4-triazol-1-yl)methane (tz2(CH2)) of the form AgX:tz2(CH2):ER3:MeCN (1:1:1:x) (X = NO3, R = Ph, E = P, As, or Sb, x = 1 or 2; X = NO2, ClO4, O3SCF3, E = P, R = Ph, x = 0, 1 or 2; X = NO3, ClO4, E = P, R = cy, x = 1; X = ClO4, E = As, R = Ph, x = 2) and AgNO3:tz2(CH2):P(o-tolyl)3 (2:2:1) have been synthesized and characterized in the solid state and in solution by analyses, spectral (IR, far-IR, 1H and 13C NMR, ESI MS data) data, and conductivity measurements. In the one-dimensional polymers (characterized by X-ray studies) AgNO3:tz2(CH2):PPh3:CH3CN (1:1:1:1), AgClO4:tz2(CH2):PPh3:CH3CN (1:1:1:2), AgNO3:tz2(CH2):AsPh3: CH3CN (1:1:1:2), and AgNO3:tz2(CH2):SbPh3:CH3CN (1:1:1:2), the silver atom can be regarded as four-coordinate, the tz2(CH2) ligands behaving as bridging groups rather than chelates, with no pair of ligands being dominant, quasi-trans, in their interactions. The AgNO3:tz2(CH2):P(o-tolyl)3 (2:2:1) adduct is a two-dimensional polymer containing two independent silv...

Bis(1,2,4-triazol-1-yl)methane)silver(I) Phosphino Complexes: Structures and Spectroscopic Properties of Mixed-Ligand Coordination Polymers.

Poly(benzotriazolyl)borates—I. ligand synthesis and characterization

Unexpected regiochemistry in the reaction of benzotriazole with KBH4: synthesis of a new class of poly(azolyl)borate ligands

The reaction of KBH4 with molten benzotriazole leads to the formation of a series of poly(benzotriazoly)borate anions [HnB(C6H4N3)4−n]− where n = 2, 1 and 0 depending on the temperature. The regiospecificity of the process differs from that of pyrazole/BH4− reactions in the BN bond-formation takes place in a manner that maximises steric crowding at boron (i.e. at the triazole N(1) atoms). The complex-forming abilities of the new ligands have been investigated, and show some interesting differences from those of the poly(1-pyrazolyl)borate analogues.

S. Miller

Papers

Poly(benzotriazolyl)borates—I. ligand synthesis and characterization

Unexpected regiochemistry in the reaction of benzotriazole with KBH4: synthesis of a new class of poly(azolyl)borate ligands

Unexpected Regiochemistry in the Reaction of Benzotriazole with KBH4: Synthesis of a New Class of Poly(azolyl)borate Ligands.