Transition metal complexes with metal−carbon multiple bonds have attracted
considerable interest in recent decades. These complexes can be prepared from terminal
alkynes. For example, reactions of [RuCl
2(PPh
3)
3] and related compounds with H≡CR or
HC≡CC(OH)RR’ can give rise to vinylidene or allenylidene complexes; treatments of
[OsCl
2(PPh
3)
3] with HC≡CC(OH)RR’ in the absence of hydrochloric acid can produce
allenylidene and carbyne complexes; treatment of [OsCl
2(PPh
3)
3] with HC≡CC(OH)RR’ in the
presence of hydrochloric acid can produce osmium vinylcarbyne complexes.
We have explored the chemistry to prepare rhenium carbyne complexes. Reactions of
[Re(dppm)
3I] (2.1, dppm = Ph
2PCH
2PPh
2) with terminal alkynes HC≡CC(OH)RR’ in the
presence of hydroiodic acid produced vinyl carbyne co...[
Read more ]
Transition metal complexes with metal−carbon multiple bonds have attracted
considerable interest in recent decades. These complexes can be prepared from terminal
alkynes. For example, reactions of [RuCl
2(PPh
3)
3] and related compounds with H≡CR or
HC≡CC(OH)RR’ can give rise to vinylidene or allenylidene complexes; treatments of
[OsCl
2(PPh
3)
3] with HC≡CC(OH)RR’ in the absence of hydrochloric acid can produce
allenylidene and carbyne complexes; treatment of [OsCl
2(PPh
3)
3] with HC≡CC(OH)RR’ in the
presence of hydrochloric acid can produce osmium vinylcarbyne complexes.
We have explored the chemistry to prepare rhenium carbyne complexes. Reactions of
[Re(dppm)
3I] (2.1, dppm = Ph
2PCH
2PPh
2) with terminal alkynes HC≡CC(OH)RR’ in the
presence of hydroiodic acid produced vinyl carbyne complexes [ReI{≡CCH=CRR’}(dppm)
2]I
(2.7). In the absence of hydroiodic acid, the reactions produced expected vinylidene complexes
ReI{=C=CH-C(OH)RR’}(dppm)
2 (2.4) a minor amount of unexpected products derived from
P−C and C−C bond cleavage.
Unexpected products derived from β-alkynyl elimination of alkoxide rhenium
complexes were produced in the reactions of 2.1 with internal alkynes. Treatments of 2.1 with
internal alkynes RC≡CC(OH)R’R’’ in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, an organic base) gave ReI(=C=CHR)(dppm)
2 (2.2) and ketones C(O)R’R’’.
Unexpected products derived from cleavage of the coordinated dppm ligand were
produced in the reactions of 2.1 with terminal internal alkynols. Treatments of
[Re(dppm)
3]BPh
4 (2.9) with the terminal alkyne HC≡CC(OH)Ph
2 in the presence of DBU
produced the P−C cleaved complex [Re{η
2-HC≡CC(Ph)
2O–PPh
2–}(PMePh
2)(dppm)]BPh
4
(4.2a) as a major product.
Reactions of carbyne complexes with nucleophiles such as alcohols, amines,
phosphines, and thiocyanates usually give carbene complexes by addition reactions. It is also
reported that sodium borohydride (NaBH
4) attacks regiospecifically on the γ-carbon of the
vinylcarbyne ligand of the complex [ReCp*(CO)
2{≡CCH=CMe
2}]BF
4 to give
[ReCp*(CO)
2{=C=C(H)CHMe
2}]. We have studied the reactivity of our newly synthesized
carbyne, vinylidene and allenylidene complexes with NaBH
4. Reactions of NaBH
4 with
[ReI{≡CCH=CRR’}(dppm)
2]I (2.7), ReI(=C=CHR)(dppm)
2 (2.4) and ReI(=C=C=CPh
2)-
(dppm)
2 (2.11a) produced unexpected rhenium borane complexes Re(η
2-H
2BHR)(dppm)
2.
Apart from the study of complexes with a rhenium−carbon multiple bond, we have also
explored the chemistry of complexes with a rhenium−nitrogen multiple bond. Treatments of
ReCl
3(PMePh
2)
3 (6.1) with organonitriles RCN, afforded the azavinylidene ReCl
3-{=N=C(PMePh
2)R}(PMePh
2)
2 (6.2). By the reaction of 6.1 with acetonitrile NCMe, we can
isolate the organonitrile intermediate, ReCl
3(NCMe)(PMePh
2)
2 (6.3d). The result implies that
azavinylidene complexes 6.2 are formed by nucleophilic addition of phosphine PMePh
2 to
ReCl
3(NCR)(PMePh
2)
2 (6.3).
Post a Comment