Group 4 alane complex

Figure 10 Group 4 alane complexes featuring additional supporting "tethers" between aluminium and titanium/zirconium. ...

The first group 13 (IIIA) element-carbene complex to be reported was an imi-dazol-2-ylidene-alane complex (Scheme 8.23). Based on NMR data, it was suggested that the imidazole fragment has an electronic structure that is intermediate between those of the free carbene and imidazolium ion. The use of an imidazol-2-... 

Another group of isoprene polymerization catalysts is based on alanes and TiCl. In place of alkyl aluminum, derivatives of AlH (alanes) are used and react with TiCl to produce an active catalyst for the polymerization of isoprene. These systems are unique because no organometaHic compound is involved in producing the active species from TiCl. The substituted alanes are generally complexed with donor molecules of the Lewis base type, and they are Hquids or soHds that are soluble in aromatic solvents. The performance of catalysts prepared from AlHCl20(C2H )2 with TiCl has been reported (101). 

When Group VI carbonyl complexes were reacted with alane or Cp2NbH3 reduction of CO to ethylene was noted.- - Ethylene was the primary product of the Cp2NbH3 reduction although it subsequently was hydrogenated to ethane. Masters and co-workers suggested that ethylene was formed through an alkylidene dimerization as shown below. 

Butterfly Cluster Complexes of the Group VIII Transition Metals Sargeson, Alan M., see Hendry, Philip Sanon, G., see Fleischauer, P. D. Sawyer, Donald T., see Sobkowiak, Andrzej Sawyer, Jeffery F., and Gillespie, Ronald J., The Stereochemistry of SB (HI) 35 437... 

R3Si709(0H)3], with group 13 metalorganics MR3 have been investigated in detail. In particular, reactions of alanes RxA1H3 x (x= 1-3) have been studied,624 yielding novel heterocyclic and cluster-type complexes. 

A further synthetic approach to carbon-metal double bonds is based on the acid-catalyzed abstraction of alkoxy groups from a-alkoxyalkyl complexes [436 -439] (Figure 3.11). These carbene complex precursors can be prepared from alk-oxycarbene complexes (Fischer-type carbene complexes) either by reduction with borohydrides or alanates [23,55,63,104,439-445] or by addition of organolithium compounds (nucleophilic addition to the carbene carbon atom) [391,446-452]. 

Reduction of unsaturated ketones to unsaturated alcohols is best carried out Nit v complex hydrides. a,/3-Unsaturated ketones may suifer reduction even at the conjugated double bond [764, 879]. Usually only the carbonyl group is reduced, especially if the inverse technique is applied. Such reductions are accomplished in high yields with lithium aluminum hydride [879, 880, 881, 882], with lithium trimethoxyaluminum hydride [764], with alane [879], with diisobutylalane [883], with lithium butylborohydride [884], with sodium boro-hydride [75/], with sodium cyanoborohydride [780, 885] with 9-borabicyclo [3.3.1]nonane (9-BBN) [764] and with isopropyl alcohol and aluminum isopro-... 

However, initial experiments with this reagent gave poor results, with the secondary amide undergoing reduction along with the tertiary amide. Compound 101 [and 107, Fig. (29)] is sufficiently twisted such that the gem-dimethyl groups effectively block the (j-face of the tertiary amide, leaving the a-face relatively unencumbered. However, a modification of the alane procedure [60], proved satisfactory for this transformation. The piperazinedione 101 was pretreated with AlEt3, with the expectation that this Lewis acid would form a complex with the more exposed secondary lactam [106, Fig.(29).] and leave the tertiary lactam accessible for reduction. 

Milione et al. reacted the same phenoxyimino functionalised imidazolium salt with trialkyl alanes in an attempt to form the corresponding carbene complex of aluminium(III) [71] (see Figure 4.19). Reaction of the phenoxyimino functionalised imidazolium salt with AIMOj proceeds smoothly with the hydroxy group reacting with the alane under elimination of methane. The imidazolium end does not react under methane elimination, but remains pendant. Aluminium carbene adducts are still rare [72-75] and are usually synthesised by a reaction between the alane and the free carbene. 

Hydride, either binary or complex, reductions of organic functional groups are expensive routes to C—H bonds, consequently such reactions are used only for specialty chemical and expensive product (pharmacueticals, etc.) synthesis. Reactions as described in 1.6.4 and 1.6.5 are used. Commonly used reactions involve NaH, KH, bo-ranes, alanes, silanes and occasionally stannanes. Detailed discussions of hydride reductions can be found in standard treatises on organic chemistry - - . Molecular rearrangement ... 

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