Influence of Ring Methylation in Group 15 Tetramethylcyclopentadienyl Complexes, M(C₅Me₄H)_nI_3−n (M = As, Sb)

Abstract

Arsenic and antimony triiodide react with 3 equiv of Na[C 5 Me 4 H] in THF to form the yellow tris(tetramethylcyclopentadienyl) derivatives M(C 5 Me 4 H) 3 in 61% and 76% yields, respectively. When equimolar amounts of SbI 3 and Na[C 5 Me 4 H] react in THF, the orange diiodo species Sb(C 5 Me 4 H)I 2 is produced in 87% yield. The effect on the complexes of the methylated cyclopentadienyl rings varies from minimal to substantial. For example, the properties of the antimony compound Sb(C 5 Me 4 H) 3 are similar to those of the unsubstituted complex Sb(C 5 H 5 ) 3 ; in contrast, As(C 5 Me 4 H) 3 and Sb(C 5 Me 4 H)I 2 are considerably more thermally stable than their parent versions. The complexes are fluxional on the 1 H NMR time scale at room temperature. A single-crystal X-ray structure of As(C 5 Me 4 H) 3 reveals three σ-bound rings with strongly localized bonding. The As-C distances are nearly identical, averaging 2.033(3) A ˚, and the C-As-C angles range from 96.4°to 109.3°. The antimony structure is similar, with average Sb-C bonds of 2.238(6) A ˚and C-Sb-C angles from 93.6°to 107.7°. The diiodo complex Sb(C 5 Me 4 H)I 2 displays an η 3 -bound ring and forms a coordination polymer in the solid state, with ordering driven by intermolecular I 3 3 3 I 0 and Me 3 3 3 Me 0 van der Waals attractions. The structures of As(C 5 H 5 ) 3 , As(C 5 Me 4 H) 3 , and Sb(C 5 H 5 ) 3 were examined with density functional theory calculations; these indicate that the energy barrier for haptotropic rearrangements is roughly the same in the arsenic compounds, 12-15 kcal mol -1 , but is about half that for the antimony complex.

Assigning Hapticity to Cyclopentadienyl Derivatives of Antimony and Bismuth

“…The slippage for σ-bonded ligands will depend on the radius of the metal, and the overall distance of the metal from the Cp ligand will dictate the magnitude of the angle θ. compounds of the tetramethylcyclopentdienyl ligand. 37 The Δ C−C value for 2b is less than for the η 1 (σ)-bonded rings of BiCp 3 (except the ligand involved in π bonding to a second Bi atom of a neighboring molecule, Figure 11a), indicating greater delocalization around the ring, consistent with a π component to the metal−Cp bond.…”

“…In 2b they alternate around the C 5 ring, with a range of 1.351(5)–1.428(6) Å corresponding to a Δ C–C value of 0.08 Å. This parameter has been used to indicate the relative delocalization of π-electron density in arsenic and antimony compounds of the tetramethylcyclopentdienyl ligand . The Δ C–C value for 2b is less than for the η 1 (σ)-bonded rings of BiCp 3 (except the ligand involved in π bonding to a second Bi atom of a neighboring molecule, Figure a), indicating greater delocalization around the ring, consistent with a π component to the metal–Cp bond.…”

“…Derivatives of the cyclopentadienyl anion have been used previously in the organometallic chemistry of antimony, and structurally characterized examples of neutral ,, and cationic , compounds have been reported, showing a range of hapticities for the [C 5 R 5 ] − ring. Most relevant to this discussion are the cyclotetrastibine [SbCp*] 4 , the trimetallic Sb/Cr compound Sb(Cp*){Cr(CO) 5 } 2 , and the chloro species SbCp*Cl 2 and SbCp* 2 Cl; geometric data for these compounds are presented alongside that of 3a in Table .…”

Structural Distortions in M[E(SiMe3)2]3 Complexes (M = Group 15, f-Element; E = N, CH): Is Three a Crowd?

“…In the course of our work on cyclopentadienyl complexes of the group 15 elements, we had occasion to examine the homoleptic bis­(trimethylsilyl)­amido complexes as well. Bi­[N­(SiMe 3 ) 2 ] 3 is a long-known compound and has been used to prepare amorphous BiO x and the ferroelectric perovskite SrBi 2 Ta 2 O 9 .…”

Nitrogen, phosphorus, arsenic, antimony and bismuth

“…103 The reaction of EI 3 (E = As, Sb) with three equivalents of Na[C 5 Me 4 H] has been shown to afford compounds E(C 5 Me 4 H) 3 . 104 Although fluxional in solution, the solid state-structure of these compounds shows a localised cyclopentadienyl group with the unsubstituted carbon atom bound to the Group 15 element. The related compound Sb(C 5 Me 4 H)I 2 was also reported which contained an Z 3 -bound ring in the solid state.…”