Synthesis and Reactions of a Hybrid Tristibine Ligand

The tripodal tristibine N­(CH₂-2-C₆H₄SbMe₂)₃ (L) has been prepared in high yield and characterized by ¹H and ¹³C­{¹H} NMR spectroscopy and elemental analysis. A range of reactions with transition-metal acceptors were carried out to probe the coordinative properties of L. The 3/1 M/L complex [{FeCp­(CO)₂}₃(L)-κSb:κSb′:κSb″]­[BF₄]₃ involves tridentate bridging coordination of L to three CpFe­(CO)₂ fragments. In [Mn­(CO)₃(L)]­[CF₃SO₃] the ligand adopts a tridentate chelating mode via a Sb₃ donor set; treatment of this complex with Me₃NO in MeCN solution gave crystals of [Mn­(CO)₂(L)­(MeCN)]­[CF₃SO₃], which lost MeCN in vacuo, probably resulting in coordination of CF₃SO₃^– coordination of the [CF₃SO₃]⁻ anion. [M­(L)]­[BF₄] (M = Ag, Cu) were also prepared. The reaction of L with CuBr leads to isolation of [Cu₄Br₄(L)₂] in the solid state, which contains a Cu₂Br₄ core with a short central Cu···Cu distance, capped with Cu­(L) units at each end. The transition-metal complexes of L were characterized by elemental analysis, ESI⁺ mass spectrometry, IR spectroscopy, and ¹H, ¹³C­{¹H}, and (where appropriate) ⁵⁵Mn or ⁶³Cu NMR spectroscopy. Solid-state X-ray structures were determined for [Mn­(CO)₃(L)]­[CF₃SO₃], [Mn­(CO)₂(L)­(MeCN)]­[CF₃SO₃], [Cu₄Br₄(L)₂], and [Cu₃Br₂(L)₂]­[BF₄]. In each of these structures the chelating ligand adopts a twisted, propeller-like conformation. NMR spectroscopic analysis suggests that the ligand also adopts this rigid conformation in solution.