Tricarbonyliron Complexes - Observation of 13C(CO) NMR Signals via Polarization Transfer

Improvements in the detection of 13C(CO) res­ onances by using polarization transfer techniques, based on long-range coupling constants "7(13C (CO )1H) = 1 ±0.1 Hz (n > 3), are reported. Coupling constants between 13C(CO) and other rare spin-1/2 nuclei have been observed, and longrange 13C (C O )-’H coupling have been traced by two-dimensional (2D ) 13C/'H heteronuclear shift correlations (HETCOR). Seven tricarbonyliron complexes 1 to 5 serve as examples in which the [Fe(CO)3] fragment is linked to cyclic dienes (siloles: la, b; l,l'-spirobisilole: 2), and to cyclic het­ erodienes derived from substituted 2,5-dihydro2,5-silaboroles [1-aza (3a, b); 1-thia (4); 1-selena (5)]. In the case of complex 5, it was possible to resolve the 77Se satellites with 2/ ( 77S e13C(CO)) = 4.4 Hz. In 2D 13C (CO )/’H HETCOR experi­ ments it was shown that polarization transfer originates mainly from C-methyl groups [4/ ( 13C (CO )1H(M e))], adjacent to the “terminal” carbon atom(s) of the cyclic diene or heterodiene system which are linked to the [Fe(CO)3] fragment.