Symmetric and non-symmetric dinuclear alkenyl-bridged carbene complexes ofchromium and tungsten

Treatment of (CO)(5)W=C(NMe2)CH=CH-Ar-(OH)(H)C=CH (1a-b) [a: -Ar- =1,4-C6H4 -; b: -Ar- = 2,5-C4H2S-] with W(CO)(5)(THF) in methanol yields the nonsymme trical bis(alkenylcarbene)-bridged ditungsten complexes (CO)(5)W=C(NMe2)CH= CH-Ar-CH=CH(OMe)C=W(CO)(5) (3a-b). Similarly, the symmetrical bis(methoxyca rbene)ditungsten derivative [(CO)(5)W=C(OMe)CH=CH-](2)(1,4-C6H4-) (4a) is o btained in a low yield from the precursor (CO)(5)W=C(OMe)CH=CH-C6H4-(OH)(H) C=CH (2a). Complexes 3a and 3b undergo aminolysis reactions with diamines s uch as piperazine and ethylenediamine to produce the corresponding bis[alke nyl(amino)carbene]ditungsten complexes 5a-b and 6a-b. The reaction of 1a wi th Cr(CO)5(THF) affords the heterobimetallic (W-Cr) bis(carbene) complex (C O)(5)W= C(NMe2)CH=CH-Ar-CH=CH(OMe)C=Cr(CO)(5) (3'a). This complex, as well as the bis(methoxycarbene) derivative 4'a, can also be obtained by treatmen t of (CO)(5)W=C(XR)CH=CH-C6H4-CHO [1c: XR = NMe2; 2c: XR = OMe] with (CO)(5 )Cr=C(OMe)CH2-Li+. All the new compounds have been characterized by analyti cal and spectroscopic methods, and the single-crystal structures of 3a, 4a- b, and 4'a have been established.