Synthesis and Structural Studies of peri-Substituted Acenaphthenes with Tertiary Phosphine and Stibine Groups.

Two mixed peri-substituted phosphine-chlorostibines, Acenap(PiPr2)(SbPhCl) and Acenap(PiPr2)(SbCl2) (Acenap = acenaphthene-5,6-diyl) reacted cleanly with Grignard reagents or nBuLi to give the corresponding tertiary phosphine-stibines Acenap(PiPr2)(SbRR') (R, R' = Me, iPr, nBu, Ph). In addition, the Pt(II) complex of the tertiary phosphine-stibine Acenap(PiPr2)(SbPh2) as well as the Mo(0) complex of Acenap(PiPr2)(SbMePh) were synthesised and characterised. Two of the phosphine-stibines and the two metal complexes were characterised by single-crystal X-ray diffraction. The peri-substituted species act as bidentate ligands through both P and Sb atoms, forming rather short Sb-metal bonds. The tertiary phosphine-stibines display through-space J(CP) couplings between the phosphorus atom and carbon atoms bonded directly to the Sb atom of up to 40 Hz. The sequestration of the P and Sb lone pairs results in much smaller corresponding J(CP) being observed in the metal complexes. QTAIM (Quantum Theory of Atoms in Molecules) and EDA-NOCV (Energy Decomposition Analysis employing Naturalised Orbitals for Chemical Valence) computational techniques were used to provide additional insight into a weak n(P)→σ*(Sb-C) intramolecular bonding interaction (pnictogen bond) in the phosphine-stibines.

Constrained Phosphine Chalcogenide Selenoethers Supported by peri-Substitution.

A series of phosphorus and selenium peri-substituted acenaphthene species with the phosphino group oxidized by O, S, and Se has been isolated and fully characterized, including by single-crystal X-ray diffraction. The P(V) and Se(II) systems showed fluxional behavior in solution due to the presence of two major rotamers, as evidenced with solution NMR spectroscopy. Using Variable-Temperature NMR (VT NMR) and supported by DFT (Density Functional Theory) calculations and solid-state NMR, the major rotamers in the solid and in solution were identified. All compounds showed a loss of the through-space JPSe coupling observed in the unoxidized P(III) and Se(II) systems due to the sequestration of the lone pair of the phosphine, which has been previously identified as the major contributor to the coupling pathway.

Phosphine and Selenoether peri-Substituted Acenaphthenes and Their Transition-Metal Complexes: Structural and NMR Investigations.

A series of peri-substituted acenaphthene-based phosphine selenoether bidentate ligands Acenap(iPr2P)(SeAr) (L1-L4, Acenap = acenaphthene-5,6-diyl, Ar = Ph, mesityl, 2,4,6-trisopropylphenyl and supermesityl) were prepared. The rigid acenaphthene framework induces a forced overlap of the phosphine and selenoether lone pairs, resulting in a large magnitude of through-space 4JPSe coupling, ranging from 452 to 545 Hz. These rigid ligands L1-L4 were used to prepare a series of selected late d-block metals, mercury, and borane complexes, which were characterized, including by multinuclear NMR and single-crystal X-ray diffraction. The Lewis acidic motifs (BH3, Mo(CO)4, Ag+, PdCl2, PtCl2, and HgCl2) bridge the two donor atoms (P and Se) in all but one case in the solid-state structures. Where the bridging motif contained NMR-active nuclei (11B, 107Ag, 109Ag, 195Pt, and 199Hg), JPM and JSeM couplings are observed directly, in addition to the altered JPSe in the respective NMR spectra. The solution NMR data are correlated with single-crystal diffraction data, and in the case of mercury(II) complexes, they are also correlated with the solid-state NMR data and coupling deformation density calculations. The latter indicate that the through-space interaction dominates in free L1, while in the L1HgCl2 complex, the main coupling pathway is via the metal atom and not through the carbon framework of the acenaphthene ring system.

Synthetic and Structural Study of peri-Substituted Phosphine-Arsines.

A series of phosphorus-arsenic peri-substituted acenaphthene species have been isolated and fully characterised, including single crystal X-ray diffraction. Reactions of EBr3 (E = P, As) with iPr2PAcenapLi (Acenap = acenaphthene-5,6-diyl) afforded the thermally stable peri-substitution supported donor-acceptor complexes, iPr2PAcenapEBr23 and 4. Both complexes show a strong P→E dative interaction, as observed by X-ray crystallography and 31P NMR spectroscopy. DFT calculations indicated the unusual As∙∙∙As contact (3.50 Å) observed in the solid state structure of 4 results from dispersion forces rather than metallic interactions. Incorporation of the excess AsBr3 in the crystal structure of 3 promotes the formation of the ion separated species [iPr2PAcenapAsBr]+Br- 5. A decomposition product 6 containing the rare [As6Br8]2- heterocubane dianion was isolated and characterised crystallographically. The reaction between iPr2PAcenapLi and EtAsI2 afforded tertiary arsine (BrAcenap)2AsEt 7, which was subsequently lithiated and reacted with PhPCl2 and Ph2PCl to afford cyclic PhP(Acenap)2AsEt 8 and acyclic EtAs(AcenapPPh2)2 9.

A Study of Through-Space and Through-Bond JPP Coupling in a Rigid Nonsymmetrical Bis(phosphine) and Its Metal Complexes.

A series of representative late d-block metal complexes bearing a rigid bis(phosphine) ligand, iPr2P-Ace-PPh2 (L, Ace = acenaphthene-5,6-diyl), was prepared and fully characterized by various techniques, including multinuclear NMR and single-crystal X-ray diffraction. The heteroleptic nature of the peri-substituted ligand L allows for the direct observation of the JPP couplings in the 31P{1H} NMR spectra. Magnitudes of JPP are correlated with the identity and geometry of the metal and the distortions of the ligand L. The forced overlap of the phosphine lone pairs due to the constraints imposed by the rigid acenaphthene skeleton in L results in a large 4 JPP of 180 Hz. Sequestration of the lone pairs, either via oxidation of the phosphine or via metal chelation, results in distinct changes in the magnitude of JPP. For tetrahedral d10 complexes ([LMCl2], M = Zn, Cd, Hg), the JPP is comparable to or larger than (193-309 Hz) that in free ligand L, although the P···P separation in these complexes is increased by ca. 0.4 Å (compare to free ligand L). The magnitude of JPP diminishes to 26-117 Hz in square planar d8 complexes ([LMX2], M = Ni, Pd, Pt; X = Cl, Br) and the octahedral Mo0 complex ([LMo(CO)4], 33 Hz). Coupling deformation density calculations indicate the through-space interaction dominates in free L, while in metal complexes the main coupling pathway is via the metal atom.

Dealkanative Main Group Couplings across the peri-Gap.

Here, we highlight the ability of peri-substitution chemistry to promote a series of unique P-P/P-As coupling reactions, which proceed with concomitant C-H bond formation. This dealkanative reactivity represents an interesting and unexpected expansion to the established family of main-group dehydrocoupling reactions. These transformations are exceptionally clean, proceeding essentially quantitatively at relatively low temperatures (70-140 °C), with 100% diastereoselectivity in the products. The reaction appears to be radical in nature, with the addition of small quantities of a radical initiator (azobis(isobutyronitrile)) increasing the rate dramatically, as well as altering the apparent order of reaction. DFT calculations suggest that the reaction involves dissociation of a phosphorus centered radical (stabilized by the peri-backbone) to the P-P coupled product and a free propyl radical, which carries the chain. This unusual reaction demonstrates the powerful effect that geometric constraints, in this case a rigid scaffold, can have on the reactivity of main group species, an area of research that is gaining increasing prominence in recent years.

Geminally Substituted Tris(acenaphthyl) and Bis(acenaphthyl) Arsines, Stibines, and Bismuthine: A Structural and Nuclear Magnetic Resonance Investigation.

Tris(acenaphthyl)- and bis(acenaphthyl)-substituted pnictogens (iPr2P-Ace)3E (2-4) (E = As, Sb, or Bi; Ace = acenaphthene-5,6-diyl) and (iPr2P-Ace)2EPh (5 and 6) (E = As or Sb) were synthesized and fully characterized by multinuclear nuclear magnetic resonance (NMR), high-resolution mass spectrometry, elemental analysis, and single-crystal X-ray diffraction. The molecules adopt propeller-like geometries with the restricted rotational freedom of the sterically encumbered iPr2P-Ace groups resulting in distinct NMR features. In the tris(acenaphthyl) species (2-4), the phosphorus atoms are isochronous in the (31)P{(1)H} NMR spectra, and the rotation of the three acenaphthyl moieties around the E-Cipso bond is locked. On the other hand, the bis(acenaphthyl) species show a fluxional behavior, resulting in an AX to A2 spin system transition in the (31)P{(1)H} variable-temperature NMR spectra. This allowed elucidation of remarkable through-space couplings ((8TS)JPP) of 11.5 Hz (for 5) and 25.8 Hz (for 6) at low temperatures. In addition, detailed line shape analysis of the thermodynamic parameters of the restricted rotation of the "propeller blades" in 5 was performed in the intermediate temperature region and also at coalescence. The lone pairs on the pnictogen atoms in 2-6 are oriented such that they form a bowl-shaped area that is somehow buried within the molecule.

Structural, spectroscopic and computational examination of the dative interaction in constrained phosphine-stibines and phosphine-stiboranes.

A series of phosphine-stibine and phosphine-stiborane peri-substituted acenaphthenes containing all permutations of pentavalent groups -SbCln Ph4-n (5-9), as well as trivalent groups -SbCl2 , -Sb(R)Cl, and -SbPh2 (2-4, R=Ph, Mes), were synthesised and fully characterised by single crystal diffraction and multinuclear NMR spectroscopy. In addition, the bonding in these species was studied by DFT computational methods. The P-Sb dative interactions in both series range from strongly bonding to non-bonding as the Lewis acidity of the Sb acceptor is decreased. In the pentavalent antimony series, a significant change in the P-Sb distance is observed between -SbClPh3 and -SbCl2 Ph2 derivatives 6 and 7, respectively, consistent with a change from a bonding to a non-bonding interaction in response to relatively small modification in Lewis acidity of the acceptor. In the Sb(III) series, two geometric forms are observed. The P-Sb bond length in the SbCl2 derivative 2 is as expected for a normal (rather than a dative) bond. Rather unexpectedly, the phosphine-stiborane complexes 5-9 represent the first examples of the σ(4) P→σ(6) Sb structural motif.

Peri-substituted phosphorus-tellurium systems-an experimental and theoretical investigation of the P···Te through-space interaction.

A series of peri-substituted phosphorus-tellurium systems R'Te-Acenap-PR2 (R' = Ph, p-An, Nap, Mes, Tip; Acenap = acenaphthene-5,6-diyl (-C12H8); R = (i)Pr, Ph) exhibiting large "through-space" spin-spin coupling constants and the "onset" of three-center four-electron type interactions is presented. The influence of the substituents at the phosphorus and tellurium atoms as well as their behavior upon oxidation (with S, Se) or metal-coordination (Pt, Au) is discussed using NMR spectroscopy, single-crystal X-ray diffraction, and advanced density functional theory studies including NBO, AIM, and ELI-D analyses.

Sterically encumbered tin and phosphorus peri-substituted acenaphthenes.

A group of sterically encumbered peri-substituted acenaphthenes have been prepared, containing tin moieties at the 5,6-positions in 1-3 ([Acenap(SnR3)2], Acenap = acenaphthene-5,6-diyl; R3 = Ph3 (1), Me3 (2); [(Acenap)2(SnMe2)2] (3)) and phosphorus functional groups at the proximal peri-positions in 4 and 5 ([Acenap(PR2)(P(i)Pr2)] R2 = Ph2 (4), Ph((i)Pr) (5)). Bis(stannane) structures 1-3 are dominated by repulsive interactions between the bulky tin groups, leading to peri-distances approaching the sum of van der Waals radii. Conversely, the quasi-linear CPh-P···P three-body fragments found in bis(phosphine) 4 suggest the presence of a lp(P)-σ*(P-C) donor-acceptor 3c-4e type interaction, supported by a notably short intramolecular P···P distance and notably large JPP through-space coupling (180 Hz). Severely strained bis(sulfides) 4-S and 5-S, experiencing pronounced in-plane and out-of-plane displacements of the exocyclic peri-bonds, have also been isolated following treatment of 4 and 5 with sulfur. The resulting nonbonded intramolecular P···P distances, ∼4.05 Å and ∼12% longer than twice the van der Waals radii of P (3.60 Å), are among the largest ever reported peri-separations, independent of the heteroatoms involved, and comparable to the distance found in 1 containing the larger Sn atoms (4.07 Å). In addition we report two metal complexes with square planar [(4)PtCl2] (4-Pt) and octahedral cis-[(4)Mo(CO)4] (4-Mo) geometries. In both complexes the bis(phosphine) backbone is distorted, but notably less so than in bis(sulfide) 4-S. All compounds were fully characterized, and except for bis(phosphine) 5, crystal structures were determined.

Reactivity profile of a peri-substitution-stabilized phosphanylidene-phosphorane: synthetic, structural, and computational studies.

The reactions of peri-substitution-stabilized phosphanylidene-phosphorane 1 with [AuCl(tht)] or [PtCl2(cod)] afford binuclear complexes [((1)(AuCl)2)2] 2 and [((1)(PtCl2))2] 3, in which four electrons of the ligand are used in bonding to two metal atoms in the bridging arrangement. Reactions of 1 with [Mo(CO)4(nbd)] or (RhCl2Cp*)2 afford mononuclear complexes [(1)2Mo(CO)4] 4 and [(1)RhCl2Cp*] 5, in which two electrons of the ligand are used to form terminal complexes. Formation of these complexes disrupts the negative hyperconjugation at the P-P bond to various extents, which is mirrored by variations in their P-P bond distances (2.179(4)-2.246(4) Å). The P-P bond is ruptured upon formation of Pd diphosphene complex 6, which is likely to proceed through a phosphinidene intermediate. In air, 1 is fully oxidized to phosphonic acid 7. Reactions of 1 with chalcogens under mild conditions generally afford mixtures of products, from which the trithionated 8, dithionated 9, diselenated 10, and monotellurated 11 species were isolated. The bonding in the chalcogeno derivatives is discussed using DFT (B3LYP) and natural bond orbital analysis, which indicate a contribution from dative bonding in 8-10. The buttressing effect of the peri backbone is shown to be an essential factor in the formation of the single push-double-pull bis(borane) 13. This is demonstrated experimentally through a synthesis parallel to that used to make 13, but lacking the backbone, which leads to different products. The P-P bond distances in the reported products, as well as additional species, are correlated with Wiberg bond indices, showing very good agreement for a variety of bonding modes, including the negative hyperconjugation.

Geometrically enforced donor-facilitated dehydrocoupling leading to an isolable arsanylidine-phosphorane.

A proximate Lewis basic group facilitates the mild dehydrogenative P-As intramolecular coupling in the phosphine-arsine peri-substituted acenaphthene 3, affording thermally and hydrolytically stable arsanylidine-phosphorane 4 with a sterically accessible two-coordinate arsenic atom. The formation of 4 is thermoneutral due to the dehydrogenation being concerted with the donor coordination. Reaction of 4 with a limited amount of oxygen reveals arsinidene-like reactivity via formation of cyclooligoarsines, supporting the formulation of the bonding in 4 as base-stabilized arsinidene R3P→AsR.