Synthesis and structural characterisation of alkali metal complexes of heteroatom-stabilised 1,4- and 1,6-dicarbanions.

A straightforward Peterson olefination reaction between either [{(Me(2)PhSi)(3)C}Li(THF)] or in situ-generated [(Me(3)Si)(2){Ph(2)P(BH(3))}CLi(THF)(n)] and paraformaldehyde gives the alkenes (Me(2)PhSi)(2)C[double bond, length as m-dash]CH(2) () and (Me(3)Si){Ph(2)P(BH(3))}C[double bond, length as m-dash]CH(2) (), respectively, in good yield. Ultrasonic treatment of with lithium in THF yields the lithium complex {(Me(2)PhSi)(2)C(CH(2))}Li(THF)(n) (), which reacts in situ with one equivalent of KOBu(t) in diethyl ether to give the potassium salt {(Me(2)PhSi)(2)C(CH(2))}K(THF) (). Similarly, ultrasonic treatment of with lithium in THF yields the lithium complex [{Ph(2)P(BH(3))}(Me(3)Si)C(CH(2))]Li(THF)(3).2THF (). The bis(phosphine-borane) (Me(3)Si){Me(2)(H(3)B)P}CH(Me(2)Si)(CH(2)) () may be prepared by the reaction of [Me(2)P(BH(3))CH(SiMe(3))]Li with half an equivalent of ClSiMe(2)CH(2)CH(2)SiMe(2)Cl in refluxing THF. Metalation of with two equivalents of MeLi in refluxing THF yields the lithium complex [{Me(2)P(BH(3))}(Me(3)Si)C{(SiMe(2))(CH(2))}]Li(THF)(3) (), whereas metalation with two equivalents of MeK in cold diethyl ether yields the potassium complex {Me(2)P(BH(3))}(Me(3)Si)C{(SiMe(2))(CH(2))}K(2)(THF)(4) () after recrystallisation. X-Ray crystallography shows that, whereas the lithium complex crystallises as a discrete molecular species, the potassium complexes and crystallise as sheet and chain polymers, respectively.