A general synthesis and the characterization of novel alkylsubstituted
NHC-stabilized pnictogenylboranes NHC·BH2ER2
(NHC=N-heterocyclic carbene, E=P, As; R2=Me2, Ph2, tBuH,
Cy2, (SiMe3)2) are reported. These compounds were reacted with
Ni(CO)4 to the corresponding complexes of the type
[(NHC ·BH2ER2)Ni(CO)3] to determine their donor strength by
Tolman Electronic Parameters (TEPs) and their steric demand as
ligands compared to classical phosphines, superbasic phosphines
and other commonly applied donor systems. The results
show that the NHC-stabilized pnictogenyltrielanes can be
considered as being highly basic, while their steric influence
depends strongly on the organic residues as well as the donor
attached to the {BH2} moiety. Although weaker than commonly
used superbasic phosphines, the donor strength of pnictogenyltrielanes
in general can be classified as of similar strength as
NHCs. The steric and electronic properties can easily be
modified by alkyl substitution as evident from the TEP trends.