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When parahydrogen is used as a source of nuclear spin polarization, spontaneous magnetization transfer has proceeded in low magnetic field from the two nascent hydride ligands of the dihydride complex fac,cis-[Ir(P[Cy.sub.3])[(py).sub.3][(H).sub.2]]B[F.sub.4] to its other NMR active nuclei. The degree of signal enhancement in the free substrate is increased by using electronically rich and sterically encumbered phosphine ligands such as P[Cy.sub.3], P[Cy.sub.2]Ph, or P[super i][Pr.sub.r] and by optimizing the strength of the magnetic field in which polarization transfer occurs.

The air-sensitive and electrochemically oxidized [Ir{ArNC(N[R.sub.2])NAr}[([C.sub.8][H.sub.14]).sub.2]] precursors ([C.sub.8][H.sub.14] = cis-cyclooctene and R = Me or Et; Ar = Ph or 4-Me[C.sub.6][H.sub.4]) were used to synthesize electron-rich tris(guanidinato) complexes of [Ir.sup.III]. The analytical and spectroscopic characterization and a single-crystal structure determination of isolable, paramagnetic [Ir.sup.IV] compounds, [Ir[{ArNC(N[R.sub.2])NAr}.sub.3]]P[F.sub.6] demonstrated the accessibility of [Ir.sup.IV] in a nitrogen-donor ligand environment.