B. Competitive Coordination of N 2 , CH 2 dCH 2 , H 2 , and CO 2 to Rhodium(I) 1769 C. CO 2 Activation−Iridium and Rhodium Formate Complexes 1770 D. Dinitrogen Controlled trans β-H Elimination 1771 E. Coordination and Oxidative Addition of H 2 O 1772 F. Reactions of Azines (R 2 CdN−NdCR 2 ) with Rh(I) Dinitrogen Complexes 1773 G. Formation and "Hydridic" Reactivity of trans-Dihydride Complexes 1774
Layer-by-layer assembly of two palladium coordination-based multilayers on silicon and glass substrates is presented. The new assemblies consist of rigid-rod chromophores connected by terminal pyridine moieties to palladium centers. Both colloidal palladium and PdCl2(PhCN)2 were used in order to determine the effect of the metal complex precursor on multilayer structure and optical properties. The multilayers were formed by an iterative wet-chemical deposition process at room temperature in air on a siloxane-based template layer. Twelve consecutive deposition steps have been demonstrated resulting in structurally regular assemblies with an equal amount of chromophore and palladium added in each molecular bilayer. The optical intensity characteristics of the metal-organic films are clearly a function of the palladium precursor employed. The colloid-based system has a UV-vis absorption maximum an order of magnitude stronger than that of the PdCl2-based multilayer. The absorption maximum of the PdCl2-based film exhibits a significant red shift of 23 nm with the addition of 12 layers. Remarkably, the structure and physiochemical properties of the submicron scale PdCl2-based structures are determined by the configuration of the approximately 15 angstroms thick template layer. The refractive index of the PdCl2-based film was determined by spectroscopic ellipsometry. Well-defined three-dimensional structures, with a dimension of 5 microm, were obtained using photopatterned template monolayers. The properties and microstructure of the films were studied by UV-vis spectroscopy, spectroscopic ellipsometry, atomic force microscopy (AFM), X-ray reflectivity (XRR), scanning electron microscopy (SEM), and aqueous contact angle measurements (CA).
Accelerated growth of a molecular-based material that is an active participant in its continuing self-propagated assembly has been demonstrated. This nonlinear growth process involves diffusion of palladium into a network consisting of metal-based chromophores linked via palladium.
Reaction of [RhCl(C 8 H 14 ) 2 ] 2 (C 8 H 14 ) cyclooctene) with 2 equiv of the aryl methyl ether phosphine 1 in C 6 D 6 results in an unprecedented metal insertion into the strong sp 2 -sp 3 aryl-O bond. This remarkable reaction proceeds even at room temperature and occurs directly, with no intermediacy of C-H activation or insertion into the adjacent weaker ArO-CH 3 bond. Two new phenoxy complexes (8 and 9), which are analogous to the product of insertion into the ArO-CH 3 bond (had it taken place) were prepared and shown not to be intermediates in the Ar-OCH 3 bond cleavage process. Thus, aryl-O bond activation by the nucleophilic Rh(I) is kinetically preferred over activation of the alkyl-O bond. The phenoxy Rh(I)-η 1 -N 2 complex ( 8) is in equilibrium with the crystallographically characterized Rh(I)-µ-N 2 -Rh(I) dimer ( 12). Reaction of [RhCl-(C 8 H 14 ) 2 ] 2 with 2 equiv of the aryl methyl ether phosphine 2, PPh 3 , and excess HSiR 3 (R ) OCH 2 CH 3 , CH 2 -CH 3 ) results also in selective metal insertion into the aryl-O bond and formation of (CH 3 O)SiR 3 . Thus, transfer of a OCH 3 group from carbon to silicon was accomplished, showing that hydrosilation of an unstrained aryl-O single bond by a primary silane is possible. The selectivity of C-O bond activation is markedly dependent on the transition-metal complex and the alkyl group involved, allowing direction of the C-O bond activation process at either the aryl-O or alkyl-O bond. Thus, contrary to the reactivity of the rhodium complex, reaction of NiI 2 or Pd(CF 3 CO 2 ) 2 with 1 equiv of 1 in ethanol or C 6 D 6 at elevated temperatures results in exclusive activation of the sp 3 -sp 3 ArO-CH 3 bond, while reaction of the analogous aryl ethyl ether 4 and Pd(CF 3 CO 2 ) 2 results in both sp 3 -sp 3 and sp 2 -sp 3 C-O bond activation. The resulting phenoxy Pd(II) complex ( 18) is fully characterized by X-ray analysis. Heating the latter under mild dihydrogen pressure results in hydrodeoxygenation to afford an aryl-Pd(II) complex (19).
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