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A DFT Study on the Stabilization of the B≡B Triple Bond in a Metallaborocycle: Contrasting Electronic Structures of Boron and Carbon Analogues
Author(s) -
Ghorai Sagar,
Jemmis Eluvathingal D.
Publication year - 2017
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.201702422
Subject(s) - triple bond , chemistry , boron , phosphine , crystallography , metal , nucleophile , chelation , stereochemistry , double bond , inorganic chemistry , organic chemistry , catalysis
The electronic structure of (η 5 ‐Cp) 2 Zr(NH 2 ‐BB‐NH 2 ) ( 3 b ) suggests that it could be a candidate for having a boron–boron triple bond in the cyclic system; however, computational studies shows that 3 b is a very high energy isomer on its potential energy surface. Replacement of amines with tricoordinate nucleophilic boron groups (η 5 ‐Cp) 2 Zr[B(PH 3 ) 2 ‐BB‐B(PH 3 ) 2 ] ( 3 c ) reduces the relative energy dramatically. The B≡B triple bond arises through the donation of two electrons from the metal fragment, ZrCp 2 , to the in‐plane π‐bonding orbital of the central B–B unit. Strong σ‐donating and chelating bis‐phosphine ligands (Me 2 P(CH 2 ) n PMe 2 ), which stabilize donor–acceptor bonding interaction in gem‐diborene L 2 B‐BBr 2 ( 10 ), would be a good choice along the synthetic path towards 3 d , (η 5 ‐Cp) 2 Zr[B 4 (Me 2 P(CH 2 ) 3 PMe 2 ) 2 ]. A comparison of the energetics of the reaction leading to a cyclic boryne system ( 3 d ), with the linear boryne isomer [(B 2 NHC Ph ) 2 ] shows that the angle strain from cyclization is compensated by stabilization from the metal.