Superior routes to ruthenium carbenes and carbynes
by Coalter, Joseph Nurnberger, III, Ph.D., Indiana University, 2000, 261 pages; AAT 3005389Advisor: Caulton, Kenneth G.
School: Indiana University
School Location: United States -- Indiana
Index terms(keywords): Ruthenium carbenes, Olefins
Source: DAI-B 62/02, p. 851, Aug 2001
Source type: Dissertation
Subjects: Chemistry
Publication Number: AAT 3005389
ISBN: 0493145737
Document URL: [url]http://proquest.umi.com/pqdweb?did=727951081&sid=2&Fmt=2&clientId=9339&RQT=309&VName=PQD[/url]
ProQuest document ID: 727951081
Abstract (Document Summary)
The reactive fragment RuHCl(P i Pr 3 ) 2 , derived from dimer [RuHCl(P i Pr 3 ) 2 ] 2 , possesses considerable reducing power from its lack of π-accepting ligands. The 14-electron nature of this fragment, which allows substrate coordination cis to an active hydride, and its powerful π-basicity facilitate a variety of novel organometallic transformations. Both vinyl ethers and amides, and allylic heterocycles are isomerized by this catalytic hydride to form coordinated carbene ligands at 25°C; this represents the simplest known preparation of heteroatom substituted carbenes. When transformed into a leaving group (as H 2 ), this hydride also facilitates the geminal dehydrogenation of aliphatic ethers and amines, a double C(sp 3 )-H bond activation to generate carbenes. The C(sp 2 )-H bond activation [of the C=C] in α,β-unsaturated aldehydes and ketones by this fragment allows the formation of highly functionalized carbenes in one-pot, where the original Ru-H becomes part of a spectroscopic probe [Ru(2H)] toward metal reducing character. Oxidative addition of the C(sp 2 )-H in DMF dramatically illustrates the π-basicity of Ru(II) devoid of π-acid ligands by formation of an unusual and isolable Ru(IV) species.
The novel hydrido-chloro carbenes RuHCl(P i Pr 3 ) 2 [=C(XR)R ' ] (X = O, NR), generated from RuHCl(P i Pr 3 ) 2 and olefins, ethers, or amines, are active initiators for ROMP of 2-norbornene, a feat previously thought impossible for heterotom-bearing carbenes. Acyclic versions of these carbenes are readily transformed to dichloro carbenes RuCl 2 (PR 3 ) 2 [=CH(Me)], useful precursors for a variety of olefin metathesis reactions, by simple treatment with HCl. This reactivity exposes an effortless route to dichloro carbenes using inexpensive vinyl ethers as the carbene source.
Two unique classes of molecules, (1) pyramidal four-coordinate carbenes Ru(OR)(PR 3 )(=CHPh) and (2) planar four-coordinate carbynes Ru(OR)(PR 3 ) 2 (≡CPh), are readily obtained by treatment of RuCl 2 (PR 3 ) 2 (=CHPh) with alkoxide or phenoxide sources; subtle interplay of sterics and electronics dictates the product identity. Analogous aliphatic carbynes Ru(X)(PR 3 ) 2 (≡CMe), also members of the second class, are available from isomeric hydrido vinylidenes RuH(X)(PR 3 ) 2 (=C=CH 2 ). The former new class is an excellent model for the elusive active species in olefin metathesis, and the latter class offers unexplored potential for alkyne metathesis.
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