Synthesis of the remarkably air- and thermally stable 2,6-diisocyano-1,3-diethoxycarbonylazulene linker from 2-amino-1,3-diethoxycarbonylazulene in 57% cumulative yield was developed. Incorporation of the ester "arms" in the design of this first diisocyanoazulene bridge permitted fully controlled stepwise installation and complexation of its isocyano junction groups. The -CO(2)Et arms in 2,6-diformamido-1,3-diethoxycarbonylazulene effectively suppress the rate of dehydration of its 2-NHCHO end relative to that of the 6-NHCHO end leading to practically exclusive formation of 6-isocyano-2-formamido-1,3-diethoxycarbonylazulene upon treatment of the above diformamide with an equimolar amount of POCl(3). This crystallographically characterized 6-isocyano-2-formamidoazulene derivative was employed to access mono- and heterobimetallic complexes of the 2,6-diisocyanoazulene scaffold with controlled orientation of the azulenic dipole. A complete series of monometallic, homobimetallic, and isomeric heterobimetallic ([M] = M(CO)(5), M = Cr and/or W) complexes of the 2,6-diisocyanoazulene motif was isolated and studied by a variety of techniques, including X-ray crystallography. The metal-to-bridge charge transfer in mono- and dinuclear adducts of 2,6-diisocyanoazulene, the assignment of which was corroborated by time-dependent density functional theory calculations, occurs at a dramatically lower energy as compared to the analogous systems featuring the 1,4-diisocyanobenzene scaffold. Moreover, the metal-to-diisocyanide charge transfer exhibits a substantially greater red shift upon binucleation of the mononuclear [M(CO)(5)] adducts of the nonbenzenoid 2,6-diisocyanoazulene linker versus the 1,4-diisocyanobenzene bridge.
The formation and properties of a new class of self-assembled monolayers (SAM) of aryl isocyanides and diisocyanides based on the nonbenzenoid azulenic framework have been investigated using FTIR spectroscopy and ellipsometry. Syntheses of several new members of the isocyanoazulene family, a recently established type of aryl isocyanides, are reported as well. The FTIR spectra for the isocyanoazulene derivatives absorbed on the gold surface indicate the terminal upright coordination of every isocyanoazulene molecule studied. In addition, the ellipsometric thicknesses have been measured and are consistent with those calculated for single monolayers of the isocyanides oriented along the surface normal. Unlike SAMs of some benzenoid aryl isocyanides, the nonbenzenoid isocyanoazule-based SAMs proved resistant to oxidation, oligomerization, and isomerization into the corresponding nitriles under ambient conditions, which is an important prerequisite to their future applications.
Contents Table 1. Crystal data Formula weight 497.66 Crystallization Solvent Not given Crystal Habit Blade Crystal size 0.39 x 0.22 x 0.09 mm 3 Crystal color Colorless Data Collection Type of diffractometer Bruker SMART 1000 Wavelength 0.71073 Å MoKα Data Collection Temperature 100(2) K θ range for 8568 reflections used in lattice determination 2.54 to 27.95° Unit cell dimensions a = 12.1774(12) Å b = 8.3901(8) Å β= 93.803(2)° c = 27.039(3) Å Volume 2756.5(5) Å 3 Z 4 Crystal system R indices (all data) R1 = 0.0900, wR2 = 0.0939 Type of weighting scheme used Sigma Weighting scheme used w=1/σ 2 (Fo 2) Max shift/error 0.000 Average shift/error 0.000 Largest diff. peak and hole 0.387 and-0.364 e.Å-3 Special Refinement Details Refinement of F 2 against ALL reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 , conventional R-factors (R) are based on F, with F set to zero for negative F 2. The threshold expression of F 2 > 2σ(F 2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Titanium and zirconium complexes supported by a bis(anilide)pyridine ligand (NNN = pyridine-2,6-bis(N-mesitylanilide)) have been synthesized and crystallographically characterized. C 2-symmetric bis(dimethylamide) complexes were generated from aminolysis of M(NMe2)4 with the neutral, diprotonated NNN ligand or by salt metathesis of the dipotassium salt of NNN with M(NMe2)2Cl2. In contrast to the case for previously reported pyridine bis(phenoxide) complexes, the ligand geometry of these complexes appears to be dictated by chelate ring strain rather than metal–ligand π bonding. The crystal structures of the five-coordinate dihalide complexes (NNN)MCl2 (M = Ti, Zr) display a C 1-symmetric geometry with a stabilizing ipso interaction between the metal and the anilido ligand. Coordination of THF to (NNN)ZrCl2 generates a six-coordinate C 2-symmetric complex. Facile antipode interconversion of the C 2 complexes, possibly via flat C 2v intermediates, has been investigated by variable-temperature 1H NMR spectroscopy for (NNN)MX2(THF) n (M = Ti, Zr; X = NMe2, Cl) and (NNN)Zr(CH2Ph)2. These complexes were tested as propylene polymerization precatalysts, with most complexes giving low to moderate activities (102–104 g/(mol h)) for the formation of stereoirregular polypropylene.
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