Chromium bimetallic complexes

The chiral bimetallic complex 1653 reacts with TMSOTf 20 in the presence of excess styrene, via 1654, to give the cyclopropane complex 1655 in high yield [38]. The chromium can be readily removed from 1655 by treatment with I2 in Et20. Analogously, the complex 1656 reacts with styrene in 90% yield, via 1657, to give MegSiOH 4 and phenylcyclopropane 1658 [39] (Scheme 10.17). 

Chromatography cyclophosphazenes, 21 46, 59 technetium, 11 48-49 Chromites, as spinel structures, 2 30 Chromium, see Tetranuclear d-block metal complexes, chromium acetylene complexes of, 4 104 alkoxides, 26 276-283 bimetallics, 26 328 dimeric cyclopentdienyl, 26 282-283 divalent complexes, 26 282 nitrosyls, 26 280-281 trivalent complexes, 26 276-280 adamantoxides, 26 320 di(/ >rt-butyl)methoxides, 26 321-325 electronic spectra, 26 277-279 isocyanate insertion, 26 280 substitution reactions, 26 278-279 [9]aneS, complexes, 35 11 atom... 

Mirkin and coworkers reported on catalytic molecular tweezers used in the asymmetric ring opening of cyclohexene oxide. In this case the early transition metal is the catalyst and rhodium functions as the structural inductor metal. The catalyst consists of two chromium salen complexes, the reaction is known to be bimetallic, and a switchable rhodium complex, using carbon monoxide as the switch. Indeed, when the salens are forced in dose proximity in the absence of CO the rate is twice as high and the effect is reversible [77]. 

Furthermore, the successful [3+2+1] cycloaddition of alkynes bearing a cyclopropane ring and a carbene complex unit has been reported. These benzannulations result in the formation of bimetallic naphthohydroquinone chromium tricarbonyl complexes [48]. Additionally, (non-strained) cyclic alkynes are potent reaction partners in the cycloaddition of chromium carbene complexes [49]. 

The earliest Ziegler-Natta catalysts were insoluble bimetallic complexes of titanium and aluminum. Other combinations of transition and Group I-III metals have been used. Most of the current processes for production of high-density polyethene in the United States employ chromium complexes bound to silica supports. Soluble Ziegler-Natta catalysts have been prepared, but have so far not found their way into industrial processes. With respect to stereo-specificity they cannot match their solid counterparts. 

The advantage of using lithiated arene complexes of chromium as starting materials to synthesize o-,7r-bimetallic complexes of chromium and manganese was clearly demonstrated by reacting (77 -o-C6H4XLi)Cr(CO)3 (X = H, F) with Mn(CO),Br (305). The products, (77< -C6H4XC(0) Mn-... 

Iron carbene complexes bearing chirality at the carbene ligand can be generated from optically pure bimetallic (chromium-iron) complexes by the addition of 1 equiv of TMSOTf in the presence of an olefin, which in situ undergoes an asymmetric cyclopropa-nation. Excellent ee s are obtained when the reaction is carried out with em-disubstituted olefins (eq 122). 5... 

Figure 10 Selectively excited luminescence spectra for a bimetallic chromium(III) complex, [(Bispicam)-Cr (0H)2(S04)Cr (Bispicam)]S206 3H20, where Bispicam denotes 7V,7V -bis(2-pyridylmethyl)-amine. The traditional, unselectively excited luminescence spectrum is shown as trace (a). Traces (b) to (e) denote selectively excited luminescence spectra from specific subsets of molecules (reproduced by permission of Elsevier Science from Chem. Phys. Lett. 1987, 133, 429-432).

Chromocene and nido-5,6-B2BgH,2 form the bimetallic chromium complex ... 

Pair-of-dimer effects, chromium, 43 287-289 Palladium alkoxides, 26 316 7t-allylic complexes of, 4 114-118 [9JaneS, complexes, 35 27-30 112-16]aneS4 complexes, 35 53-54 [l5]aneS, complexes, 35 59 (l8)aneS4 complexes, 35 66-68 associative ligand substitutions, 34 248 bimetallic tetrazadiene complexes, 30 57 binary carbide not reported, 11 209 bridging triazenide complex, structure, 30 10 carbonyl clusters, 30 133 carboxylates... 

The insertion of various isocyanates into chromium(lll) alkoxide M—O bonds has been reported.737 The complexes are prepared by refluxing the isocyanates with a suspension of the alkoxide in benzene. No structural data were given for the products. Unusual bimetallic alkoxides have recently been prepared738 by the reaction of Cr[Al(OPr )4]3 with alcohols and acetylacetone (166). A wide range of spectroscopic methods were used to study them. In general, the results were in accord with a monomeric formulation similar to (166) below Cr[Al(OMe)4]3 was grossly insoluble the small size of the methyl groups may permit extensive polymerization. 

The mass spectra of bimetallic carbonyl metal compounds with cyclic arsine ligands have been discussed (Table 10). Molecular ion peaks are present for the pentamethyl-cyclopentaarsine containing complexes of chromium and tungsten, (AsMe)5[M(CO)]2 (186,188). Their decomposition includes CO and/or M(CO)5 loss giving rise to the ions (AsMe)sM2(CO) + (n = 0-9), (AsMe)sM(CO)/ (n = 0-5), M As Me-" and MAs Me+ (m = 2-4), MjAs Me, M AsMe -" (m = 2-4), MAs (w = 2-5), MAsjCH and AsMOj The latter is the most abundant in the mass spectra . ... 

Supported metal complexes and clusters with well-defined structures offer the advantages of catalysts that are selective and structures that can be understood in depth. Such catalysts can be synthesized precisely with organometallic precursors, as illustrated in this review. Synthetic methods are illustrated with examples, including silica-supported chromium and titanium complexes for alkene polymerization rhodium carbonyls bonded predominantly at crystallographically specific sites in a zeolite and metal clusters, including Ir4, Rhg, OsjC, and bimetallics. 

Heterogeneous, bimetallic metathesis catalysts are formed by reactions of Fischer type carbyne tungsten or molybdenum complexes with the reduced Phillips catalyst, a suface chromium(II) compound on silica (14).(scheme 5). The bimetallic surface compounds can result from 2+1 cycloaddition reactions. Similar reactions are well known by the work of Stone (15). 

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