13C and 15N NMR Mechanistic Study of Cyanide Exchange on

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Inorg. Chem. 1998, 37, 1278-1288

13C

and 15N NMR Mechanistic Study of Cyanide Exchange on Oxotetracyanometalate Complexes of Re(V), Tc(V), W(IV), Mo(IV), and Os(VI) Amira Abou-Hamdan,1 Andreas Roodt,*,2 and Andre´ E. Merbach*,1 Institut de Chimie Mine´rale et Analytique, Universite´ de Lausanne, Baˆtiment de Chimie (BCH), Lausanne CH-1015, Switzerland, and Department of Chemistry, University of the Orange Free State, Bloemfontein 9300, South Africa ReceiVed September 30, 1997

A range of complexes with general formula [MO(X)(CN)4]n- of W(IV), Mo(IV), Re(V), Tc(V), and Os(VI) were prepared and characterized by 13C, 15N, 17O, and 99Tc NMR, utilizing 13C- and 15N-enriched cyano complexes. A correlation between M-O and M-CN bond strength from X-ray crystallographic data and |1J(183W-13C)| coupling is reported. The cyanide (HCN/CN-) exchange kinetics on the trans-dioxotetracyanometalate complexes and protonated/substituted ([MO(X)(CN)4]n-) forms thereof were studied in aqueous medium. The dioxotetracyano complexes show a trend of reactivity M(IV) > M(V) >M(VI), which is in agreement with the increase in M-L bond strength (L ) O2- or CN-) and a dissociative activation for the cyanide and the oxygen exchange in these complexes. Rate constants (X, kXc) in s-1 at 298 K for the [MO(X)(CN)4]n- complexes are as follows for Mo(IV): O2-, >0.4; OH-, (1.7 ( 0.1) × 10-2; H2O, (1.5 ( 0.1) × 10-2; CN-, (9.6 ( 0.8) × 10-3. For W(IV): O2-, (4.4 ( 0.4) × 10-3; OH-, (9.6 ( 0.9) × 10-5; H2O, (1.1 ( 0.1) × 10-4; CN-, (1.1 ( 0.1) × 10-2; N3-, (3.1 ( 0.2) × 10-4; F-, (4.8 ( 0.1) × 10-5. For Tc(V): O2-, (4.8 ( 0.4) × 10-3; H2O,