Solitaire and gemini metallocene porphyrazines

Article abstract of DOI:10.1021/ja003702x

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^IVV^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.