... metal center.(7) Typical TEP values for phosphines range from 2111 cm –1 for PF 3 (weak electron donor) to 2056 cm –1 for P(t-butyl ... vanadium,(4) chromium,(9-12) molybdenum,(4, 6, 13-16) tungsten,(4, 9, 16-19) rhenium,(20) iron,(21-28) ruthenium,(29) rhodium,(30-39) iridium ...