The preparation of the new S3 -, tetrahedral enforcer ligand, PhTt t -Bu- (phenyltris((tert-butylthio)methyl)borate), is reported as the Tl(I) salt along with its corresponding [PhTt t -Bu]CoCl and [PhTt t -Bu]NiCl complexes. Each has been characterized by X-ray diffraction. Preliminary reactivity studies demonstrate that [PhTt t -Bu]NiCl is a useful synthon for the preparation of a range of tetrahedral derivatives.

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The synthesis and characterization of a series of [RTt]2M (RTt- = tetrakis((methylthio)methyl)borate; M = Fe, Co, Ni) complexes are reported. Isostructural derivatives of the newly synthesized phenyltris((methylthio)methyl)borate (PhTt-) also have been prepared and characterized. In each case, the ligand provides tridentate, face-capping coordination to the divalent metal ion. The Fe(II) complexes exhibit spin-crossover behavior both in solution and in the solid state. For [PhTt]2Fe, the temperature dependence of μeff has been mapped between 5 K (1.3 μB) and 400 K (3.2 μB). The low-spin Co(II) derivatives exhibit characteristic axial EPR spectra; for [PhTt]2Co, g ⊥ = 2.185, g ∥ = 2.035, A ⊥ = 55 G, and A ∥ = 42 G. Using O h Fe(II) and Co(II) derivatives as benchmarks, the ligand field strength imparted by these anions is significant and falls just below that of the neutral macrocycle 1,4,7-trithiacyclononane (ttcn). All complexes have been characterized by X-ray diffraction. X-ray data:  [PhTt]2Fe·0.6Et2O, monoclinic space group C2/c, with a = 22.293(4) Å, b = 12.842(8) Å, c = 15.326(2) Å, β = 130.28(6)°, V = 3347.4(5) Å3, and Z = 4; [RTt]2Co, triclinic space group P1̄, with a = 8.396(6) Å, b = 8.850(2) Å, c = 9.124(4) Å, α = 107.43(2)°, β = 92.20(4)°, γ = 94.50(4)°, V = 643.0(3) Å3, and Z = 1; [PhTt]2Co, monoclinic space group P21/c, with a = 8.821(1) Å, b = 14.127(8) Å, c = 12.055(3) Å, β = 103.93(2)°, V = 1458.0(5) Å3, and Z = 2; [RTt]2Ni, triclinic space group P1̄, with a = 8.607(3) Å, b = 8.876(3) Å, c = 9.173(3) Å, α = 107.44(2)°, β = 92.92(2)°, γ = 93.38(2)°, V = 665.70(3) Å3, and Z = 1; [PhTt]2Ni:  triclinic space group P1̄, with a = 8.627(7) Å, b = 8.862(4) Å, c = 10.559(6) Å, α = 75.08(4)°, β = 76.64(5)°, γ = 72.71(5)°, V = 734.3(8) Å3, and Z = 1.

A series of electronically and coordinatively unsaturated four-coordinate organocobalt(II) complexes, [PhTt tBu ]Co(R) ([PhTt tBu ] ) phenyltris((tert-butylthio)methyl)borate; R ) Me, Et, Ph, Bn) have been prepared by reaction of [PhTt tBu ]CoCl with the corresponding R 2 Mg reagent. These high-spin, S ) 3/2, complexes have been characterized spectroscopically and several of their structures determined by X-ray diffraction. The R ) allyl derivative, [PhTt tBu ]Co(η 3 -allyl), is low spin. Reaction of [PhTt tBu ]Co(R) with CO yielded the acyl adducts [PhTt tBu ]Co(CO)C(O)R when R ) Me, Et, Ph. These five-coordinate, lowspin complexes possess square pyramidal stereochemistry with a thioether occupying the apical position. In contrast, [PhTt tBu ]Co(R), R ) Bn or allyl, reacted with CO generating the brown cobalt(I) dicarbonyl [PhTt tBu ]Co(CO) 2 . The latter reaction is proposed to proceed via CO-promoted Co-C bond homolysis. The Ni complex [κ 2 -PhTt tBu ]Ni(η 3 -allyl) shows no reactivity with CO under similar conditions. Each of the [PhTt tBu ]Co(R) species reacts with NO, generating brown [κ 2 -PhTt tBu ]Co(NO) 2 in good yield.