Diphosphine complexes

Keto esters are obtained by the carbonylation of alkadienes via insertion of the aikene into an acylpalladium intermediate. The five-membered ring keto ester 22 is formed from l,5-hexadiene[24]. Carbonylation of 1,5-COD in alcohols affords the mono- and diesters 23 and 24[25], On the other hand, bicy-clo[3.3.1]-2-nonen-9-one (25) is formed in 40% yield in THF[26], 1,5-Diphenyl-3-oxopentane (26) and 1,5-diphenylpent-l-en-3-one (27) are obtained by the carbonylation of styrene. A cationic Pd-diphosphine complex is used as the catalyst[27]. 

Figure 3.48 The diphosphine complexes [Pd Bu2P(CH2) PBu2 Cl2]2 and [Pt PBu2P(CH2) 2-...

Schemes 6-6 Oxidative addition of water to lr(l) diphosphine complexes 42 and 44...

Very air-sensitive iridium diphosphine complexes carrying a peraryldiphosphine ligand, [IrCl(diphosphine)]2 (42a, 42b)(a diphosphine = BPBP b diphosphine = BINAP [47, 48]) can also activate MeOH in addition to HjO at room temperature very easily. Reaction of 42 with excess MeOH in toluene at room temperature gave ah-stable and thermally stable colorless hydrido (me thoxo) complexes, [ IrH(diphos-phine) 2( 4-OMe)2( i-Cl)]Cl (69) quantitatively (Eq. 6.21) [49]. The shucture of 69b,... 

The dinuclear iridium(l) diphosphine complexes 42 can also activate carboxylic acids easily. For example, the reaction of [IrCl(binap)]2 (42b) with an excess of acetic acid or benzoic acid in toluene at room temperature gave the corresponding (hydri-... 

We also found that iridium hydrido(hydroxo) complexes like [ lrH(diphos-phine) 2( x-OH)2( x-Cl)]Cl (43) and the precursor diphosphine complexes 42 can also catalyze the hydration of nitriles. In the presence of catalyhc amounts of these complexes, heating acetonitrile and benzonitrile with excess water at 120°C gave the corresponding amides [47, 50]. 

For ruthenium, special precursors are required to synthesize defined bidentate diphosphine complexes. With Taniaphos for instance, it is possible to synthesize such complexes starting from unusual rathenium(ll) species. The complexes were characterized by NMR and single crystal analysis. 

X-ray crystallographic data for homoleptic [Ni°(L-L)2] diphosphine complexes with a NiP4 core are collected in Table 24. 

The mechanism of uptake and retention of the mono-cationic 99mTc complexes in the myocardium - or other tissues - has not been fully resolved. Most of the mechanistic studies have been conducted with 99mTc (MIBI)6f and "mTc-diphosphine complexes. It has been shown that these mono-cationic complexes are not taken up in myocytes via the Na+/K+-ATPase pump as is 201T1+ [41]. Instead, these cationic tracers are localized and retained in cellular membranes, including mitochondrial membranes [41]. 

A number of Rh1 diphosphine complexes were grafted on the surface of inorganic oxides such as zeolites132 or silica.133 In the latter case, catalysts prepared by reaction of [Rh(COD)2]BF4 with previously functionalized silicas give ee s up to 94.5% for this reaction. 

It is interesting to note that using the sol-gel procedure (I) the pre-formation of the rhodium diphosphine complex suppressed the formation of ligand free rhodium-cations on the silica surface. This approach gave rise to a well-defined, very selective hydroformylation catalyst. All immobilised catalysts were 10 to 40 times slower than the homogeneous catalyst under the same conditions, the sol-gel procedure yielding the fastest catalyst of this series. 

Addition of ketene silyl acetals to aldehydes and ketones is also mediated by achiral palladium(ll) acetate-diphosphine complexes (Equation (109)).46S,46Sa Although the precise mechanism is still unclear, high catalytic activity may be ascribed to the intermediacy of palladium enolates. 

Several accounts have described (Z)-dehydroamino acid esters as being less active than the corresponding (F)-isomer [59c, 143-145]. In fact, Bruneau and Demonchaux reported that when reduction of an (E/Z)-mixture of 73 with Rh-Et-DuPhos in THF was not complete, only unreacted (Z)-73 was detected. These findings conflict, however, with results obtained in MeOH [56 d], where the ligand structure was also found to be significant to the relative reactivity of each stereoisomer. As for a-dehydroamino acid derivatives, preformed metal-diphosphine complexes generally perform in superior fashion to those prepared in situ [56d]. 

Since there are unresolved issues in the fine detail of reaction mechanism, it is worth recalling an earlier publication on reactive intermediates in iridium hydrogenation [61]. In general, conventional Ir diphosphine complexes turnover slowly or not at all when enantioselective hydrogenation of standard substrates is attempted, and essentially all the practical and useful recent synthetic contri-... 

Enantioselectivities >90% were reported for a Ti-ebthi catalyst (Table 34.4 entry 4.1) and for some Rh-diphosphine complexes (entries 4.2-4.4). Interestingly, the highest ee-values were obtained using sulfonated diphosphines (bdppsuif) in an aqueous biphasic medium (entry 4.3). The degree of sulfonation strongly affected the enantioselectivity the Rh-mono-sulfonated bdpp gave 94% ee, compared to 65% ee with Rh-bdpp in MeOH, and almost racemic product with bis-or tris-sulfonated ligands. In addition, the activity of the mono-sulfonated cata-... 

Besides these results, we registered with interest the claim by Magee and Norton [51] that (Cp)W-diphosphine complexes are able to hydrogenate imines via a novel ionic mechanism, albeit with low ee and TOF. 

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