Boranes phosphine complexes

IS facilitated after forming the borane ( Phosphine complexes. Mainu in such complexes and enhancement adjacent carbon enable the enantios< complex. Oxidative coupling of the accomplish the synthesis of C,-symm<... 

The same phosphine-borane used for the synthesis of BisP acted as the starting materials of the construction of MiniPHOS, the next smaller analogue to BisP (Scheme 13). The chirally induced lithium salt was treated with alkylphos-phorus dichloride, methylmagnesium bromide, and borane-THF complex to afford enantiomerically pure MiniPHOS-borane 82a. Recrystallization enabled elimination of a small amount of corresponding raeso-diastereomer formed [29]. Yields were generally low, ranging from 13 to 28%. 

A catalytic cycle proposed for the metal-phosphine complexes involves the oxidative addition of borane to a low-valent metal yielding a boryl complex (35), the coordination of alkene to the vacant orbital of the metal or by displacing a phosphine ligand (35 —> 36) leads to the insertion of the double bond into the M-H bond (36 —> 37) and finally the reductive elimination to afford a hydroboration product (Scheme 1-11) [1]. A variety of transition metal-boryl complexes have been synthesized via oxidative addition of the B-H bond to low-valent metals to investigate their role in cat-... 

Silver nitrate-phosphine complexes are used to prepare borane derivatives ... 

Nucleophilic Attack at Other Atoms.- Interest has continued in the synthesis of phosphine-borane adducts. Complexes of tetramethyldiphosphine with borane and various halogenoboranes have been used to generate a series of open-chain and cyclic phosphino-boranes. Adducts of 1,3,5-diazaphosphorinanes involving two... 

Figure 8 Phosphine-borane Au complexes and associated natural localized molecular orbital. (See insert for color/color representation of this figure)...

Scheme 6 Suzuki-Miyaura cross-coupling mediated by phosphine-borane Pd complexes...

Scheme 9 Hydroboration mediated by a phosphine-borane Pd complex...

Figure 8 Phosphine-borane Au complexes and associated natural localized molecular orbital...

Phosphine complexes. Maintenance of a tetrahedral state of the phosphorus atom in such complexes and enhancement of acidity of the hydrogen atoms attached to an adjacent carbon enable the enantioselective deprotonation by the s-BuLi/(-)-sparteine complex. Oxidative coupling of the lithio derivatives and removal of the borane units accomplish the synthesis of Cj-symmetric P-chiral diphosphines. 

Although neutral, the above phosphine borane ligands contain four-coordinate boron when free and are more like BH4 ligands, i.e. more hydridic character than in the base-free HBcat complexes from which borane can be displaced as in Equation (33) to form, for example, a silane-borane o-complex. 

Nucleophilic attack at other atoms. The chemistry of phosphine-borane adducts has continued to generate interest. Simple borane adducts of primary vinyl-, ethynyl- and allenyl-phosphines have been prepared and studied by a range of spectroscopic and theoretical techniques. The same group has also shown that attachment of the BH3 unit to a variety of primary phosphines results in a substantial increase in the intrinsic acidity of the system in the gas-phase. Group III halide adducts of the type Bu 2PH EX3 (E = B, Al, Ga or In X = Cl or Br) are accessible from the reactions of the secondary phosphine with the trihalides at room temperature. The solid state structure and reactivity of these adducts was also reported. Treatment of l,8-bis(diphenylphosphino)naphthalene with the borane-dimethylsulfide complex in ether solvents affords a simple monoborane adduct of the diphosphine irrespective of the molar ratio of the... 

Since Evans et al. [78] has discovered that prochiral alkyl(dimefliyl) phosphine boranes can undergo the enantioselective deprotonation of one methyl group, using butyllithium and ( )-sparteine 141, these compounds have been widely used for the synthesis of P-chirogenic borane phosphines [79-105]. Lithium alkyls form chiral complexes 142 with sparteine 141 and related chiral diamines, which were investigated by single crystal X-ray analysis (Scheme 43) [82-87]. 

Numerous phosphine-metal-borane cage complexes have been synthesised in recent years with interest focussed on possible catalytic applications (Chapter 10). Some of these compounds with phosphine groups linked to borane cages via metal atoms are shown in Figure 9.4. 

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