Solitaire and Gemini Metallocene Porphyrazines

Abstract

We report the synthesis and physical characterization of a series of peripherally functionalized porphyrazines (pzs) of the forms H2[pz(A;B3)] and trans-H2[pz(A2);B2], where A is a dithiolene chelate of molybdocene or vanadocene and B is a solublizing group. The precursor pz's 8 and 9, of the form H2[pz(A;B3)], where A = (4-(butyloxycarbonyl)-S-benzyl)2 and B = di-tert-butylphenyl (8) or di-n-propyl (9), have been prepared, deprotected, and peripherally metalated with molybdocene and vanadocene to form 1(Mo(IV)) and 1(V(IV)), prepared from 8, and 2(Mo(IV)) from 9, respectively. Likewise, the protected trans-H2[pz(A2);B2)], where A = (S-benzyl)2 and B = 3,6-butyloxybenzene (12) or A = (S-benzyl)2 and B = (tert-butylphenyl)2 (13), have been prepared and peripherally metalated with molybdocene and vanadocene to give the trans dinuclear complexes, 3(Mo(IV),Mo(IV)), 3(V(IV),V(IV)) (from 12), and 4(V(IV),V(IV)) (from 13). A crystal structure of the trans vanadocene pz 4(V(IV),V(IV)) is presented; the distance between the two vanadium atoms is 14.5 A. The molybdocene-appended pz's are highly redox active and exhibit cyclic voltammograms that are more than just the sum of the metallocene and the parent pz's. Chemical oxidation with FcPF6 gives the Mo(V) species 1(Mo(V)), 2(Mo(V)), 3(Mo(V),Mo(IV)), and 3(Mo(V),Mo(V)). Their EPR spectra are indicative of extensive delocalization from the Mo(V) into the dithiolato-pz. The EPR spectrum of the mononuclear paramagnetic vanadocene pz, 1(V(IV)), shows an expected 8-line pattern for an S = 2 system with hyperfine coupling to a single 51V (I = 7/2) nucleus, but the dinuclear vanadocene pz's, 3(V(IV),V(IV)) and 4(V(IV),V(IV)), exhibit a striking 15-line pattern of the same breadth from the S = 1 state formed by exchange coupling between the S = 2 vanadium centers of a dinuclear complex. Thus, the porphyrazine macrocycle is capable of mediating magnetic exchange interactions between metal ions bound to the periphery, separated by 14.5 A.