Multiple bonds between main-group elements and transition metals. 77. Condensation reactions of methyltrioxorhenium(VII) with catechols and aromatic thiols

Abstract

strengthens the Os-carbonyl bond opposite the donor atom (Rh). This effect has been observed previously in related dative-bonded c o m p o~n d s .~~~~~~~The Rh-Os separation of 2.8744 (3) 8, is typical of a single bond but is not a useful indication about the nature of this interaction, especially in the presence of the bridging alkyne. This Rh-Os bond is somewhat longer than that observed (2.758 (5) 8,) in the related compound [RhOsC1zBr(p-CO)(dppm)2] ,53 which in our interpretation would have an Os-Rh donor-acceptor bond accompanied by semibridging carbonyl groups. The significant difference in these two Rh-Os distances no doubt results from the very different bridging ligands involved, with the alkyne group causing greater separation of the metals in the present case. SummaryA series of low-valent, dppm-bridged complexes involving Rh and Os are readily obtained from [RhOsH-(CO),(dppm),]. Carbonyl substitution in [RhOs(CO),-( d p~m )~] + by the poorer n-acceptor but better o-donor tBuNC ligand occurs on Os opposite the metal-metal bond, supporting our arguments that the Os-Rh bonds in these species are best regarded as donor-acceptor interactions. Carbonyl loss from the saturated Os center in the com- pounds [Rh0~(C0),(p-CO)(p-RC=CR)(dppm)~] [BF,] isaccompanied by the unusual formation of a Rh+Os dative bond, regenerating coordinative saturation at Os. This may be viewed as an example of the neighboring-group effect, with Rh assisting in labilization of a carbonyl from Os. The presence of the coordinatively unsaturated Rh center in these compounds provides a route into chemistry involving the normally inert and coordinatively saturated Os center, and it is probable that substitution reactions occur by coordination at Rh, followed by facile rearrangement. This suggestion is supported by the reactions of [RhOs(CO),(cc-RC=CR)(dppm),] [BF,] with a series of neutral and anionic ligands, in which the incoming ligands are clearly shown to be bound to the Rh center. Acknowledgment.We thank the Natural Sciences and Engineering Research Council of Canada (NSERC) and the University of Alberta for support of this work and the NSERC for partial support of the diffractometer and for an Undergraduate Student Research Award to R.A.F. We also thank Professor J. Takats for a loan of 13CO-enriched O S~( C O )~~ and Professor R. G. Cave11 for supplying a sample of NaS,PMe2.2H20.Supplementary Material Available: Listings of anisotropic thermal parameters, positional and thermal parameters for the BF4anion and CH,Cl, molecules, additional bond lengths and angles, and hydrogen atom parameters for 12 and NMR data for 9-22 (11 pages); a listing of the observed and calculated structure factors for 12 (48 pages). Ordering information is given on any current masthead page.The title compound methyltrioxorhenium(VI1) reacts with catechols to yield complexes of the formula CH3Re(0),(1,2-02C6R4) ( ( 2)) that are fully characterized as pyridine adducts 3. Conducting these reactions in the presence of nucleophiles, e.g., halides, gives the hexa...

Rhenium‐Catalyzed Deoxydehydration of Diols and Polyols

“…Among the various ways to prepare rhenium diolates, the condensation of an oxorhenium complex and a neutral diol molecule (Scheme 2) is particularly relevant for the catalytic process so this will be the main focus here. Apart from the condensation of CH 3 ReO 3 and o-catechol (a diol incapable of undergoing DODH), [35,36] this reaction was first employed by Herrmann and co-workers in 1991 for the preparation of the light-yellow CH 3 ReO 2 (pinacolate) in CH 2 Cl 2 . [37] The reversibility of the condensation was later demonstrated for the analogues CH 3 ReO 2 (perfluoropinacolate).…”

Deoxydehydration of vicinal diols by homogeneous catalysts: a mechanistic overview

“…[27] had previously demonstrated oxo-abstraction of Cp*ReO­ 3 by phosphines to form the oxo-bridged dimeric rhenium species (Cp*) 2 Re 2 O 4 . Condensation between methyltrioxorheynium (MTO) and catechols had also been previously demonstrated [28]. Finally, Gable [29] had independently synthesized reduced Cp*ReO(diolate) species and found that upon heating, the diolate undergoes cycloreversion to form alkene and Cp*ReO 3 , successfully demonstrating the final step of the DODH reaction several years before the report of the catalytic reaction.…”

High-valent Organorhenium Compounds

“…58 Other reactions that result in reduction o f (12) have been reported; for example, ZnMe 2 reacts to give [{Re(u-O)(O)Me 2 } J 44 ' 45 and polymer-bound triphenylphosphine removes an oxo ligand to form "ReO 2 Me" in situ, which can then be captured by a l k y n e 1 1 * 2 6 (Scheme 3) or reoxidized with phenanthrenequinone to give (14). 20 Ethylene glycol and pinacol react with (12) in methanol to give rhenium(VI) oxo-bridged compounds but reactions with pinacol or perfluoropinacol in CH 2 C1 2 give rhenium(VII) (IS). 5 0 * 5 9 A related water elimination reaction forms (16) in Scheme 6.…”

“…[RetNR^CTOR'jR 3 ] (R'=Bu l or Xyl, R 2 = Bu\ R 3 = CH 2 Bu l ; R'=Xyl, R 2 = CMe 2 Ph, R 3 = CH 2 CMe 2 Ph) complexes react with sources of H C 1 to yield chloro alkylidene-alkylidyne compounds (e.g., (20) via Equation (io)). 75 ' 76 ' 78 ' 79 Remarkably, the reaction in Equation (10) can even be carried out in air using aqueous HC1, illustrating the stability of the alkylidene and alkylidyne ligands in (20).…”

“…75 ' 76 ' 78 ' 79 Remarkably, the reaction in Equation (10) can even be carried out in air using aqueous HC1, illustrating the stability of the alkylidene and alkylidyne ligands in (20). There is considerable evidence that reaction (10) and similar reactions proceed by a sequence of steps that include proton transfers from the alkylidene and alkyl ligands to imido and amido ligands, respectively (i.e., Re-C multiple bonds are formed rather than Re-N multiple bonds).…”