Treatment of (CO)5W=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 nonsymmetrical bis(alkenylcarbene)‐bridged ditungsten complexes (CO)5W=C(NMe2)CH=CH−Ar−CH=CH(OMe)C=W(CO)5 (3a−b). Similarly, the symmetrical bis(methoxycarbene)ditungsten derivative [(CO)5W=C(OMe)CH=CH−]2(1,4‐C6H4−) (4a) is obtained in a low yield from the precursor (CO)5W=C(OMe)CH=CH−C6H4−(OH)(H)C≡CH (2a). Complexes 3a and 3b undergo aminolysis reactions with diamines such as piperazine and ethylenediamine to produce the corresponding bis[alkenyl(amino)carbene]ditungsten complexes 5a−b and 6a−b. The reaction of 1a with Cr(CO)5(THF) affords the heterobimetallic (W−Cr) bis(carbene) complex (CO)5W=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 treatment of (CO)5W=C(XR)CH=CH−C6H4−CHO [1c: XR = NMe2; 2c: XR = OMe] with (CO)5Cr=C(OMe)CH2−Li+. All the new compounds have been characterized by analytical and spectroscopic methods, and the single‐crystal structures of 3a, 4a−b, and 4′a have been established.
The template action of chromium is held responsible for ring closure of (1) to form the complex (2). The reaction fails to occur with the homologous tungsten compound.
Pentacarbonyl{methoxy-[1-(η5-4-methoxy-6-phenylcyclohexadienyl)tricarbonylmanganese]carbene}chromium
(5) accessible from (η5-1-bromo-4-methoxy-6-phenylcyclohexadienyl)tricarbonylmanganese
(4) and Cr(CO)6 undergoes a chromium-templated
benzannulation with 3-hexyne to give monometallic Cr complex 12 in 60% yield. The key feature of this reaction is the participation
of a conjugated double bond of the η5-cyclohexadienyl-Mn
moiety in the [3+2+1] benzannulation reaction. The X-ray structure
of complex 12 reveals a syn position
of the phenyl group with respect to the Cr tripod, supporting the
participation of the Mn moiety in the benzannulation process.
6-Chromanols were prepared via photochemical benzannulation of the α-exo-benzylidene-2-oxacyclohexylidene chromium complex 2 with various alkynes. No benzannulation reaction, however, is observed under the thermal standard conditions.
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