ABSTRACT
The synthesis of previously unknown bis(cyclopentadienyl) complexes of the first transition metal, i.e., Sc(II) scandocene complexes, has been investigated using C5H2(tBu)3 (Cpttt), C5Me5 (Cp*), and C5H3(SiMe3)2 (Cpâ³) ligands. Cpttt2ScI, 1, formed from ScI3 and KCpttt, can be reduced with potassium graphite (KC8) in hexanes to generate dark-red crystals of the first crystallographically characterizable bis(cyclopentadienyl) scandium(II) complex, Cpttt2Sc, 2. Complex 2 has a 170.6° (ring centroid)-Sc-(ring centroid) angle and exhibits an eight-line EPR spectrum characteristic of Sc(II) with Aiso = 82.6 MHz (29.6 G). It sublimes at 200 °C at 10-4 Torr and has a melting point of 268-271 °C. Reductions of Cp*2ScI and Cpâ³2ScI under analogous conditions in hexanes did not provide new Sc(II) complexes, and reduction of Cp*2ScI in benzene formed the Sc(III) phenyl complex, Cp*2Sc(C6H5), 3, by C-H bond activation. However, in Et2O and toluene, reduction of Cp*2ScI at -78 °C gives a dark-red solution, 4, which displays an eight-line EPR pattern like that of 1, but it did not provide thermally stable crystals. Reduction of Cpâ³2ScI, in THF or Et2O at -35 °C in the presence of 2.2.2-cryptand, yields the green Sc(II) metallocene iodide complex, [K(crypt)][Cpâ³2ScI], 5, which was identified by X-ray crystallography and EPR spectroscopy and is thermally unstable. The analogous reaction of Cp*2ScI with KC8 and 18-crown-6 in Et2O gave the ligand redistribution product, [Cp*2Sc(18-crown-6-κ2O,O')][Cp*2ScI2], 6, as the only crystalline product. Density functional theory calculations on the electronic structure of these compounds are reported in addition to a steric analysis using the Guzei method.
ABSTRACT
Dialuminenes RAlAlR (R = m-terphenyl or bulky aryl) react with the aromatic solvents (e.g. benzene or toluene) in which they dissolve. We synthesized -SiMe3 substituted derivatives of known terphenyl ligands to increase their solubility in alkanes which have lower reactivity than arenes. The new dialuminene was synthesized via the comproportionation reaction of Na2(AlAriPr4-4-SiMe3)2 (3) (AriPr4-4-SiMe3 = 2,6-(2,6-iPr2C6H3)2-4-SiMe3C6H2) with either the diiodide Al(Et2O)I2AriPr4-4-SiMe3 (1) or the 1,2-diiododialane 4-SiMe3AriPr4(I)Al-Al(I)AriPr4-4-SiMe3 (2). This cleanly generates the dialuminene 4-SiMe3AriPr4AlAlAriPr4-4-SiMe3 which was trapped as its cycloaddition product (4) with benzene. Even in non-aromatic, essentially inert, solvents red 4 decomposes to colorless solutions. This indicates that the instability of the free dialuminene is an inherent property rather than arising from of the method of synthesis, solvent employed, or the presence of impurities.
Subject(s)
Benzene , Toluene , SolventsABSTRACT
The reaction of :AlAriPr8 (AriPr8 = C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2) with ArMe6N3 (ArMe6 = C6H3-2,6-(C6H2-2,4,6-Me3)2) in hexanes at ambient temperature gave the aluminum imide AriPr8AlNArMe6 (1). Its crystal structure displayed short Al-N distances of 1.625(4) and 1.628(3) Å with linear (C-Al-N-C = 180°) or almost linear (C-Al-N = 172.4(2)°; Al-N-C = 172.5(3)°) geometries. DFT calculations confirm linear geometry with an Al-N distance of 1.635 Å. According to energy decomposition analysis, the Al-N bond has three orbital components totaling -1350 kJ mol-1 and instantaneous interaction energy of -551 kJ mol-1 with respect to :AlAriPr8 and ArMe6NÌ:. Dispersion accounts for -89 kJ mol-1, which is similar in strength to one Al-N π-interaction. The electronic spectrum has an intense transition at 290 nm which tails into the visible region. In the IR spectrum, the Al-N stretching band is calculated to appear at ca. 1100 cm-1. In contrast, reaction of :AlAriPr8 with 1-AdN3 or Me3SiN3 gave transient imides that immediately reacted with a second equivalent of the azide to give AriPr8Al[(NAd)2N2] (2) or AriPr8Al(N3){N(SiMe3)2} (3).
ABSTRACT
Reduction of the aluminum iodide AlI2AriPr8 (1; AriPr8 = C6H-2,6-(C6H2-2,4,6-Pri3)2-3,5-Pri2) with 5% w/w Na/NaCl in hexanes gave a dark red solution from which the monomeric alanediyl :AlAriPr8 (2) was isolated in ca. 28% yield as yellow-orange crystals. Compounds 1 and 2 were characterized by X-ray crystallography, electronic and NMR spectroscopy, and theoretical calculations. The Al atom in 2 is one-coordinate, and the compound displays two absorptions in its electronic spectrum at 354 and 455 nm. It reacts with H2 under ambient conditions to give the aluminum hydride {AlH(µ-H)AriPr8}2, probably via a weakly bound dimer of 2 as an intermediate.
ABSTRACT
The reaction of the molybdenum-molybdenum triple-bonded dimer (CO)2CpMo≡MoCp(CO)2 (Cp = η5-C5H5) with the triple-bonded dimetallynes AriPr4MMAriPr4 or AriPr6MMAriPr6 (AriPr4 = C6H3-2,6-(C6H3-2,6-Pri2)2, AriPr6 = C6H3-2,6-(C6H2-2,4,6-Pri3)2; M = Ge, Sn, or Pb) under mild conditions (≤80 °C, 1 bar) afforded AriPr4M≡MoCp(CO)2 or AriPr6M≡MoCp(CO)2 in moderate to excellent yields. The reactions represent the first isolable products from a metathesis of two metal-metal triple bonds. Analogous exchange reactions with the single-bonded (CO)3CpMo-MoCp(CO)3 gave ArMÌ-MoCp(CO)3 (Ar = AriPr4 or AriPr6; M = Sn or Pb). The products were characterized by NMR (1H, 13C, 119Sn, or 207Pb), electronic, and IR spectroscopy and by X-ray crystallography.
ABSTRACT
Simple reactions of their terphenyl lead bromide precursors with DIBAL-H in diethyl ether solution at ca. -78 °C leads to the isolation of the hydrides {Pb(µ-H)ArPri4}2 (ArPri4 = C6H3-2,6-(C6H3-2,6-Pri2)2) (1) and {Pb(µ-H)ArMe6}2 (ArMe6 = C6H3-2,6-(C6H2-2,4,6-Me3)2) (2) in good yield (60-80%). The isolated solids are stable at up to 5 °C for several weeks but are thermally labile in solution. Hydride 1 decomposes to the diplumbyne ArPri4PbPbArPri4, while 2 decomposes to the plumbylene Pb(ArMe6)2. The decomposition of 1 was determined to be zero order with a rate constant of ca. 2.0 × 10-5 M min-1 at 298 K.
ABSTRACT
A series of formally triply bonded diplumbyne analogues of alkynes of the general formula ArPbPbAr (Ar = terphenyl ligand with different steric properties) was synthesized by two routes. All diplumbyne products were synthesized by a simple reduction of the corresponding Pb(II) halide precursor ArPb(Br) by DIBAL-H with yields in the range 8-48%. For one of the diplumbynes ArPri4PbPbArPri4 (ArPri4 = C6H3-2,6-(C6H3-2,6-Pri2)2) it was shown that reduction of ArPri4Pb(Br) using a magnesium(I) beta-diketiminate afforded a much improved yield in comparison (29 vs 8%) to that obtained by reduction with DIBAL-H. The more sterically crowded diplumbyne ArPri8PbPbArPri8 (ArPri8 = C6H-3,5-Pri2-2,6-(C6H2-2,4,6-Pri3)2) displayed a shortened Pb-Pb bond with a length of 3.0382(5) Å and wide Pb-Pb-C angles of 114.73(7)° and 116.02(6)° consistent with multiple-bond character with a bond order of up to 1.5. The others displayed longer metal-metal distances and narrower Pb-Pb-C angles that were consistent with a lower bond order that approached one. Computational studies of the diplumbynes yielded detailed insight of the unusual bonding and explained their similar electronic spectra arising from the flexibility of the C-Pb-Pb-C core in solution. Furthermore, the importance of London dispersion interactions for the stabilization of the diplumbynes was demonstrated.
ABSTRACT
Reactions of the tetrylenes Ge(SAr(Me6))2 (1) (Ar(Me6) = C6H3-2,6(C6H2-2,4,6-Me3)2), and Sn(SAr(Me6))2 (2) with (Mo(CO)4(NBD) (NBD = bicyclo[2.2.1]hepta-2,5-diene) gave three new, unusual complexes [Mo(THF)(CO)3{Ge(SAr(Me6))2}] (3), [Mo(THF)(CO)3{Ge(SAr(Me6))2}] (4) and [Mo(CO)4{Sn(SAr(Me6))2}] (5) which display no significant Ge/Sn-Mo bonding. Instead the ligands are coordinated to molybdenum in a bidentate fashion via the thiolato sulfurs.
