General Route to Cyclobutadiene Rhodium Complexes

Abstract

Cyclobutadiene rhodium complexes bear high potential for applications in organometallic synthesis and catalysis. We have found that the cyclobutadiene complexes with substitutionally labile p-xylene ligands [(C4 R4 )Rh(p-xylene)](+) can be synthesized in one step from the commercially available bis(ethylene) complex [{(C2 H4 )2 RhCl}2 ], p-xylene, and internal alkynes. The replacement of p-xylene by various ligands provides a general access to other [(C4 R4 )Rh] compounds, such as [(C4 R4 )RhCl]x , [(C4 R4 )RhL3 ](+) , [(C4 R4 )Rh(C5 H5 )], and [(C4 R4 )Rh(arene)](+) . Complex [(C4 Et4 )Rh(p-xylene)](+) also catalyzes an unusual cycloisomerization of a 1,11-dien-6-yne into a bicyclic diene.

Unpredictable cycloisomerization of 1,11-dien-6-ynes by a common cobalt catalyst

“…The structures of the starting dienyne 1h and the cyclohexene trans - 2b were established by X-ray crystallography. The structures of cis - 2b and 3b had been reported previously [11,43]. …”

“…These compounds were also obtained using a 1,2-bis(diphenylphosphino)benzene (dppbz) ligand. Despite the extensive studies of enyne transformations, this type of cyclization has been achieved only recently, using a cyclobutadiene rhodium complex as a catalyst [43]. …”

Diverse ring-opening reactions of rhodium η4-azaborete complexes

“…It should be emphasized that the intermediacy of azaboretes in these reactions stands in sharp contrast to the reactions of all-carbon analogues in this regardwhereas ve-membered metallacyclopentadiene derivatives 17 are believed to be key reaction intermediates in the trimerization of alkynes, the corresponding h 4 -cyclobutadiene complexes 18,19 resulting from reductive elimination are highly stable and thought to be Scheme 1 Simplified representation of the metal-catalyzed synthesis of (hetero)arenes by trimerization of alkyne derivatives.…”

Prediction of the structural and spectral properties and reactivity of the silicon analogs of cyclobutadiene C4-nSinH4 (n=0-4) by density functional theory computations

“…As another application of this molecule, it is a part of different medicine structures [8]. In recent years, many scientists had tried to solve the instability and antiaromaticity problems of this annulene by entering silicon atoms in the structure of cyclobutadiene [9,10]. This comes back to the weakness and high reactivity of silicon pi bonds.…”

“…So, one can hope that the silicon analogs of this molecule would have had more applications than cyclobutadiene compound. In last decades, various attempts were done for preparation of these analogs [7][8][9][10][11], but its chemistry is very novel and needs more researches to complete the understanding their structures and applications. So, the present study aims at providing some useful information about the structural and spectral properties, reactivity, and natural bond orbital (NBO) population analysis of the cyclobutadiene molecule and its silicon analogs.…”