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A Mechanistic Study of the Utilization of arachno ‐Diruthenaborane [(Cp*RuCO) 2 B 2 H 6 ] as an Active Alkyne‐Cyclotrimerization Catalyst
Author(s) -
Geetharani K.,
Tussupbayev Samat,
Borowka Julia,
Holthausen Max C.,
Ghosh Sundargopal
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201200291
Subject(s) - alkyne , chemistry , catalysis , yield (engineering) , cycloaddition , quantum chemical , reaction conditions , medicinal chemistry , stereochemistry , molecule , physics , organic chemistry , thermodynamics
The reaction of nido ‐[1,2‐(Cp*RuH) 2 B 3 H 7 ] ( 1 a , Cp*=η 5 ‐C 5 Me 5 ) with [Mo(CO) 3 (CH 3 CN) 3 ] under mild conditions yields the new metallaborane arachno ‐[(Cp*RuCO) 2 B 2 H 6 ] ( 2 ). Compound 2 catalyzes the cyclotrimerization of a variety of internal‐ and terminal alkynes to yield mixtures of 1,3,5‐ and 1,2,4‐substituted benzenes. The reactivities of nido ‐ 1 a and arachno ‐ 2 with alkynes demonstrates that a change in geometry from nido to arachno drives a change in the reaction from alkyne‐insertion to catalytic cyclotrimerization, respectively. Density functional calculations have been used to evaluate the reaction pathways of the cyclotrimerization of alkynes catalyzed by compound 2 . The reaction involves the formation of a ruthenacyclic intermediate and the subsequent alkyne‐insertion step is initiated by a [2+2] cycloaddition between this intermediate and an alkyne. The experimental and quantum‐chemical results also show that the stability of the metallacyclic intermediate is strongly dependent on the nature of the substituents that are present on the alkyne.