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Synthesis of 6,6′‐Bis(dimethylamino)‐ and 6,6′‐Dibromo‐Substituted 2,2′‐Diphosphanylbiphenyls and Their Palladium Complexes
Author(s) -
Petzold Holm,
Alrawashdeh Albara I. S.,
Heider Silvio,
Haufe Linda,
Rüffer Tobias
Publication year - 2013
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201300473
Subject(s) - chemistry , palladium , ligand (biochemistry) , medicinal chemistry , phenylboronic acid , adduct , lone pair , coordination sphere , catalysis , isopropyl , stereochemistry , crystallography , crystal structure , molecule , organic chemistry , biochemistry , receptor
New 6,6′‐dibromo‐ and 6,6′‐bis(dimethylamino)‐substituted 2,2′‐diphosphanylbiphenyl ligands 11 – 14 were prepared starting from 2,2′‐dibromo‐4,4′‐dimethyl‐6,6′‐dinitro‐1,1′‐biphenyl ( 4 ). Depending on the phosphane groups [diphenylphosphanyl ( 11 , 13 ) or diisopropylphosphanyl ( 12 , 14 )] the palladium dichloride complexes show different coordination symmetry. Whereas the smaller diphenylphosphanyl groups lead to C 2 ‐symmetric complexes, the respective bis(diisopropyl)phosphanes 12 and 14 form C 1 ‐symmetric complexes that show fluxional behavior due to the restricted rotation of the isopropyl groups as well as the exchange of atom positions within the C 1 ‐symmetric conformer. All complexes have been tested as precatalysts in the Suzuki–Miyaura cross coupling reaction of 2‐bromotoluene and phenylboronic acid. The activity of the catalytic system increases with the size of the diphosphanes and the donating ability of the ligand. In contrast to C 2 ‐symmetric palladium complex 15 , platinum complex 19 was found to be C 1 ‐symmetric in the solid state despite the fact that both complexes have the small bis(diphenylphosphanyl)‐substituted diphosphane ligand 11 in common. NiBr 2 adduct 20 with a similar diphosphane 13 exists as a mixture of distorted square‐planar and tetrahedral coordination sphere geometries in equilibrium with each other.