Modular synthesis of diphosphoramidite ligands derived from 1,8,10,9-triazaboradecalin and their complexes with Ni, Pd, and Pt

Abstract

Here we report a convenient synthesis of new diphosphoramidite ligands derived from 1,8,10,9-triazaboradecalin (TBD) and describe their complexes with group 10 metals. Treating the chlorinated and structurally characterized ligand precursor ClTBDPhos (L1) with four equivalents of HOR (R = C3H7 or C3HF6) in the presence of NEt3 yielded the diphosphoramidite ligands iPrOTBDPhos (L2) and F-iPrOTBDPhos (L3) in good yields. L2 and L3 were used to prepare a variety of Ni, Pd, and Pt complexes with chloride and 1,2-benzenedithiolate ligands so their structures and spectroscopic properties could be compared to similar complexes with methoxy-substituted MeOTBDPhos such as (MeOTBDPhos)PdCl2, which is reported here for the first time. Single-crystal XRD studies on the (ROTBDPhos)PtCl2 complexes revealed that increasing the size of alkoxy substituents from MeO to iPrO to F-iPrO decreases the P-M-P bite angle from 97.47(3)° in (MeOTBDPhos)PtCl2 to 93.98(4)° in (F-iPrOTBDPhos)PtCl2. Similar changes were observed in the dithiolate complexes (iPrOTBDPhos)Pt(S2C6H4) and (F-iPrOTBDPhos)Pt(S2C6H4), and the structural studies revealed longer Pt-P bond distances compared to the dichloride complexes that correlated to ca. 1000 Hz decrease in their 195Pt-31P coupling constants. No significant changes were observed in the ligand bond distances in complexes containing the methoxy and isoproxy-substituted ligands, but complexes with fluorinated F-iPrOTBDPhos revealed subtle, but significant differences in their P-N, P-O, and B-N distances that reflect substituent-induced electronic changes in the ligand. Overall, this work establishes a more convenient synthetic entry into the chemistry of alkoxy-substituted TBDPhos ligands for ongoing studies with these and related transition metal complexes.