Adamantyl phosphine

The reaction between 2-adamantyl halides and PCl /AlBr yields a mixture of di-2-adamantylphosphinic chloride and bromide together with (1-adamanyl)(2-adamantyl)phosphinic chloride 1-adamantyl halides are already known to afford only 1-adamantylphosphonic acid derivatives. 

Plenio et al. tested an adamantyl phosphine ligand bound to soluble polystyrene (Figure 4.43) in various palladium-catalyzed C-C coupling reactions.[62] The retention of metal complexes of the polymer-bound phosphine ligand were determined to be higher than 99.95%. 

Figure 4.43. Polymer-bound adamantyl phosphine ligands.[62]...

A general method for preparation of ArCOAr from ArB(OH)2, Ar Br and CO employs Pd(OAc)2, butylbis(l-adamantyl)phosphine and TMEDA. ... 

NaaCOs, affords high yields in the reaction of 4-chloroanisole (71) with -butyl acrylate (38) in DMA at 140 °C. This is likely to be the highest temperature that has appeared in literature for hgand-accelerated Mizoroki-Heck reactions of unreactive aryl chlorides. In the same protocol, several bulky secondary phosphines, namely bis(adamantyl)phosphine, bis(norbomyl)phosphine and f-BuaPH, were also operative yet inferior to f-BusP [133]. Unlike the Hartwig-Fu protocol, this method has found no application so far, which is why its scope cannot be reliably assessed. 

More recently, an improved protocol for palladium-catalyzed alkoxycarbony-lation of aryl chlorides with alkyl formates was developed by Beller and colleagues [225]. In the presence of palladium(II) acetate/n-butylbis(l-adamantyl)phosphine, and l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a base, for the first time non-activated chloroarenes could be conveniently carbonylated in good yields (Scheme 2.28). In this report, it has been shown that the catalyst system presented does not need the presence of ruthenium co-catalysts. 

In 1993 Burk, Brown, and coworkers confirmed that DuPHOS complexes exhibit the same anti-lock-and-key mechanistic motif as seen for aryl phosphine ligated catalysts [41], In 1998 by Burk and coworkers reported an unexpected and interesting result [34], With substrates having R<, = aryl, selectivity of 99% e.e. for the S product resulted from (S,S)-Me-DuPHOS-Rh hydrogenations, but the R product was obtained with similarly high enantioselectivity when Ra = t-Bu or adamantyl. In other words, the simple change of an aryl substituent to a bulky alkyl completely reverses the sense of enantioselection. 

Calorimetric measurements in solution support these observations A relative enthalpy scale for different NHCs coordinated to ruthenium(II) [Eq. (40)] shows that NHCs have a higher donor capability than the best phosphine donor ligands. The only exception is the sterically extremely demanding l,3-di(l-adamantyl)imida-zolin-2-ylidene (Table III). The enthalpies for the formation of sulfur adducts... 

Almost simultaneously, several groups developed efficient procedures for Heck reactions of deactivated chloroarenes 22 involving sterically crowded monodentate phosphines as activating ligand on the palladium (Scheme 11) [31]. Littke and Fu employed commercially available P(t-Bu)3, Hartwig P(t-Bu)3 or bis-t-butyl-ferroce-nylphosphine, and Beller di(l-adamantyl)-n-butylphosphine. The use of biscyclo-hexylmethylamine as the base instead of alkali metal carbonates or phosphates significantly extends the scope of the Fu procedure in respect of the olefin partner. 

Fig. 10 Phosphine ligands assembled to the periphery of a urea adamantyl-functionalized poly(propylene imine) dendrimer 33...

Excellent activities in the coupling of all kinds of aryl chlorides were achieved by use of catalyst 13 containing the bulky bis(adamantyl)( -butyl)phosphane. TONS of 10 to 2 X 10 were recorded even for non-activated aryl chlorides [23]. Quite recently, phosphine oxides according to the equilibrium in eq. (4) were used with Pd2(dba)3 in the Suzuki coupling of aryl chlorides, while a hydroxyphosphine complex/Ni(COD)2 catalyzes the Kumada coupling of the same substrates [26],... 

M. Beller has also developed a similar bulky mono-dentate phosphine ligand, di( 1 -adamantyl)- -butyIphosphine, for the coupling of aryl chlorides. 56 Although (Ad)2P(w-Bu) allows for the arylation of bulky anilines and secondary amines, as well as f-BuNH2, the reaction temperatures are significantly higher (100-120 °C). In addition, electron neutral or rich aryl chlorides couple best, whereas electron deficient aryl chlorides were not extensively reported. 

NHC = Al-heterocyclic carbene PtoH = tris(o-tolyl)phosphine SIAd = l,3-bis(l-adamantyl)-4-5-dihydroimidazol-2-ylidene SIMes = l,3-dimesityl-4,5-dihydroimidazol-2-ylidene SIPr = l,3-bis(2,6-diisopropylphenyl)-4,5-dihydro-imidazol-2-ylidene THF = tetrahydrofuran TM = transition metal tmed = Al,Al,Al, Al -tetramethylethylenediamine ... 

Many further examples of the interaction of PCI3 or dichlorophosphines RPCI2 in sulphuric acid with a wide range of adamantane substrates, variously substituted, have been reported when the products are the adamantylphosphonic dichlorides or [adamantyl(R)] phosphinic chlorides, respectively. 

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