Phosphido-borane complexes of group I and II metals

Abstract

The synthesis and characterisation of a range of novel phosphine-borane precursors is described: {(Me3Si)2CH}PH(C6H4-2-CH2OMe)(BH3) (39), {(Me3Si)2CH}PH(C6H4-2- SMe)(BH3) (40), {(Me3Si)2CH}PH(C6H4-2-OMe)(BH3) (41) and {(Me3Si)2CH}PH(C6H5)(BH3) (42). Treatment of 39 with n-BuLi, BnNa or BnK proceeds cleanly to give the corresponding alkali metal complexes, which are crystallised in the presence of THF, tmeda and pmdeta, respectively, to yield the adducts [[{(Me3Si)2CH}P(BH3)(C6H4-2-CH2OMe)]ML]2 [ML = Li(THF), (49); ML = Na(tmeda), (50); ML = K(pmdeta), (51)]. Deprotonation of 40 with n-BuLi, BnNa or BnK, followed by crystallisation in the presence of THF, tmeda or pmdeta, respectively, yields the compounds [{(Me3Si)2CH}P(BH3)(C6H4- 2-SMe)M(L)]n [ML = Li(THF), n = 2 (64); ML = Na(tmeda), n = ∞ (65); ML = K(pmdeta), n = 2 (66)]. On heating a solution of 64 in the presence of free phosphine-borane 40, concurrent formation of the corresponding phosphine [{(Me3Si)2CH}PH(C6H4-2-SMe)] (45) and phosphido-bis(borane) [{(Me3Si)2CH}P(C6H4-2-SMe)(BH3)2Li] (72) is observed via multinuclear NMR spectroscopy. Treatment of 41 with n-BuLi, BnNa or BnK, yield the corresponding phosphido-boranes. Heating a solution of the lithium salt [{(Me3Si)2CH}P(C6H4-2-OMe)(BH3)Li(THF)] (85) in toluene, in the presence of one equivalent of tmeda yields the unexpected phosphinesubstituted lithium alkoxide [{(Me3Si)CH}PH(C6H4-2-O)Li]6 (89) and the tertiary phosphineborane {(Me3Si)2CH}PMe(BH3)(C6H4-2-OMe) (90), and a third unidentified phosphoruscontaining compound. Repeating the experiment with the analogue [{(Me3Si)2CH}P(C6H4-2- OMe)(BD3)Li(THF)n] (104), and monitoring the reaction using 2D and 31P{1H} NMR spectroscopy, indicates that the source of the P-H proton is the borane group. It was also found that heating a solution of 85 in toluene, in the presence of an excess of THF and one equivalent of tmeda results in another thermolytic reaction pathway, generating 90 and a phosphorus-containing compound, proposed to be the alkoxo-phosphido-borane [{(Me3Si)2CH}P(BH3)(C6H4-2-O)Li2(tmeda)2] (91). Reaction between CaI2 and two equivalents of [{(Me3Si)2CH}P(C6H4-2-OMe)(BH3)]K yields the cluster [{(Me3Si)2CH}P(C6H4-2-O)(BH3)Ca(THF)]4 (108) and 90. 108 crystallises with an unusual Ca4O4 core, with two distinct calcium environments. Reaction between 42 and n-BuLi, BnNa or BnK proceeds cleanly to give the corresponding alkali metal phosphido-boranes. The lithium salt crystallises in the presence of THF as a polymer [{(Me3Si)2CH}P(C6H5)(BH3)Li(THF)2]∞ (115), whilst the sodium salt crystallises in the presence of 12-crown-4 as the solvent-separated ion species [{(Me3Si)2CH}P(C6H5)(BH3)][Na(12-crown-4)2] (116). The potassium salt crystallises in the presence of pmdeta as the adduct [{(Me3Si)2CH}P(C6H5)(BH3)K(pmdeta)]2 (117). The reaction between 42 and PhCH2K followed by addition of half an equivalent of either SrI2 or BaI2, generates the corresponding alkaline-earth metal complexes [{(Me3Si)2CH}P(C6H5)(BH3)]2Sr (119) and [{(Me3Si)2CH}P(C6H5)(BH3)]2Ba (120). A series of alkaline and alkaline earth metal phosphido-bis(borane) complexes have been prepared. The reaction between 42 and one equivalent of n-BuLi, PhCH2Na or PhCH2K, followed by addition of BH3·SMe2, yields the corresponding phosphido-bis(borane) complexes. The lithium salt is crystallised in the presence of one equivalent of 12-crown-4 to yield the monomer [{(Me3Si)2CH}P(C6H5)(BH3)2Li(12-crown-4)] (123), whilst the sodium and potassium salts are crystallised in the presence of THF to yield the adducts [{(Me3Si)2CH}P(C6H5)(BH3)2Na(THF)2]2 (124) and [{(Me3Si)2CH}P(C6H5)(BH3)2 K(THF)2]∞ (125). Deprotonation of 41 with PhCH2Na followed by reaction with BH3·SMe2 yields the corresponding salt, which is crystallised in the presence of 12-crown-4 as a solventseparated ion pair [{(Me3Si)2CH}P(C6H4-2-OMe)(BH3)2][Na(12-crown-4)2] (126). Treatment of two equivalents of 42 with one equivalent of either MgBu2, CaBn2 or {(Me3Si)2CH}2Sr, followed by addition of BH3·SMe2 yield the corresponding salts, which are crystallised in the presence of THF as the adducts [[{(Me3Si)2CH} P(BH3)2(C6H5)]2Mg(THF)4], (128), [[{(Me3Si)2CH}P(BH3)2(C6H5)]2Ca(THF)4] (129) and [[{(Me3Si)2CH}P(BH3)2(C6H5)]2Sr(THF)4] (130), respectively.