Introducing NacNac-Like Bis(4,6-isopropylbenzoxazol-2-yl)methanide in s‑Block Metal Coordination

Within this work, the field of bulky methanides in metal coordination is exceeded by the synthesis of the versatile and promising bis­(4,6-isopropylbenzoxazol-2-yl)­methane (<b>7</b>) ligand platform. As an enhancement in this class of ligands, isopropyl (<i>i</i>Pr) substituents as steric-demanding groups have been successfully introduced in proximity to the coordination pocket, mimicking the shielding abilities of the ubiquitous NacNac ligand scaffold to improve the steric protection of a coordinated s-block metal cation. A percent buried volume (% V_bur) calculation as well as an electronic structure analysis shades light onto the shielding and electronic abilities of the ligand in comparison to other selected methanides and diketiminates. Upon deprotonation with a variety of different group 1 and 2 metalation agents, a row of novel s-block metal complexes of the parent deprotonated monoanionic ligand <b>7</b> was obtained and structurally, as well as spectroscopically, characterized. In particular, in this context, the alkali-metal precursor complexes [Li­(THF)₂{(4,6-<i>i</i>Pr-NCOC₆H₂)₂CH}] (<b>8</b>) and [K­{μ-(4,6-<i>i</i>Pr-NCOC₆H₂)₂CH}]_∞ (<b>9</b>) as well as the alkaline-earth-metal compounds [MgCl­(THF)₂{(4,6-<i>i</i>Pr-NCOC₆H₂)₂CH}] (<b>10</b>) and [M­(THF)_n{(4,6-<i>i</i>Pr-NCOC₆H₂)₂CH}₂] [M = Mg, <i>n</i> = 0 (<b>11</b>); M = Ca, <i>n</i> = 1 (<b>12</b>); M = Sr, <i>n</i> = 1 (<b>13</b>); M = Ba, <i>n</i> = 1 (<b>14</b>)] were successfully synthesized. Especially, the latter four exhibit interesting trends in the solid state as well as in solution within the metal series

Solution Structures of Hauser Base ^<i>i</i>Pr₂NMgCl and <i>Turbo</i>-Hauser Base ^<i>i</i>Pr₂NMgCl·LiCl in THF and the Influence of LiCl on the Schlenk-Equilibrium

Grignard reagents that are at the simplest level described as “RMgX” (where R is an organic substituent and X a halide) are one of the most widely utilized classes of synthetic reagents. Lately, especially Grignard reagents with amido ligands of the type R₁R₂NMgX, so-called Hauser bases, and their <i>Turbo</i> analogue R₁R₂NMgX·LiCl play an outranging role in modern synthetic chemistry. However, because of their complex solution behavior, where Schlenk-type equilibria are involved, very little is known about their structure in solution. Especially the impact of LiCl on the Schlenk-equilibrium was still obscured by complexity and limited analytical access. Herein, we present unprecedented insights into the solution structure of the Hauser base ^<i>i</i>Pr₂NMgCl <b>1</b> and the <i>Turbo</i>-Hauser base ^<i>i</i>Pr₂NMgCl·LiCl <b>2</b> at various temperatures in THF-<i>d</i>₈ solution by employing a newly elaborated diffusion ordered spectroscopy (DOSY) NMR method hand-in-hand with theoretical calculations

Effects of Metal Coordination on the π‑System of the 2,5-Bis-{(pyrrolidino)-methyl}-pyrrole Pincer Ligand

Pincer complexes of 2,5-bis­{(pyrrolidino)-methyl}-pyrrole with group 14 elements such as germanium, tin, and lead were prepared and fully characterized by X-ray single-crystal analysis, NMR spectroscopy, and mass spectrometry. The structures of the complexes were analyzed and compared to the free and the lithiated ligand to gain insight into the effects of metal coordination on the aromatic system. A further aspect was to elaborate the capability of group 14 metals to interact with the pyrrole π-system. Therefore, electronic structure calculations were carried out with group 14 complexes to better understand the bonding situation and the trends among the group. The changes in the aromaticity of the pyrrole ring upon coordination have been rationalized according to the interaction of the π-system with the metal. The unusual short bond distance observed between germanium and the coordinated pyrrole nitrogen was also assessed

Effects of Metal Coordination on the π‑System of the 2,5-Bis-{(pyrrolidino)-methyl}-pyrrole Pincer Ligand

Pincer complexes of 2,5-bis­{(pyrrolidino)-methyl}-pyrrole with group 14 elements such as germanium, tin, and lead were prepared and fully characterized by X-ray single-crystal analysis, NMR spectroscopy, and mass spectrometry. The structures of the complexes were analyzed and compared to the free and the lithiated ligand to gain insight into the effects of metal coordination on the aromatic system. A further aspect was to elaborate the capability of group 14 metals to interact with the pyrrole π-system. Therefore, electronic structure calculations were carried out with group 14 complexes to better understand the bonding situation and the trends among the group. The changes in the aromaticity of the pyrrole ring upon coordination have been rationalized according to the interaction of the π-system with the metal. The unusual short bond distance observed between germanium and the coordinated pyrrole nitrogen was also assessed

Effects of Metal Coordination on the π‑System of the 2,5-Bis-{(pyrrolidino)-methyl}-pyrrole Pincer Ligand

Pincer complexes of 2,5-bis­{(pyrrolidino)-methyl}-pyrrole with group 14 elements such as germanium, tin, and lead were prepared and fully characterized by X-ray single-crystal analysis, NMR spectroscopy, and mass spectrometry. The structures of the complexes were analyzed and compared to the free and the lithiated ligand to gain insight into the effects of metal coordination on the aromatic system. A further aspect was to elaborate the capability of group 14 metals to interact with the pyrrole π-system. Therefore, electronic structure calculations were carried out with group 14 complexes to better understand the bonding situation and the trends among the group. The changes in the aromaticity of the pyrrole ring upon coordination have been rationalized according to the interaction of the π-system with the metal. The unusual short bond distance observed between germanium and the coordinated pyrrole nitrogen was also assessed

Effects of Metal Coordination on the π‑System of the 2,5-Bis-{(pyrrolidino)-methyl}-pyrrole Pincer Ligand

Pincer complexes of 2,5-bis­{(pyrrolidino)-methyl}-pyrrole with group 14 elements such as germanium, tin, and lead were prepared and fully characterized by X-ray single-crystal analysis, NMR spectroscopy, and mass spectrometry. The structures of the complexes were analyzed and compared to the free and the lithiated ligand to gain insight into the effects of metal coordination on the aromatic system. A further aspect was to elaborate the capability of group 14 metals to interact with the pyrrole π-system. Therefore, electronic structure calculations were carried out with group 14 complexes to better understand the bonding situation and the trends among the group. The changes in the aromaticity of the pyrrole ring upon coordination have been rationalized according to the interaction of the π-system with the metal. The unusual short bond distance observed between germanium and the coordinated pyrrole nitrogen was also assessed

Carbene-Dichlorosilylene Stabilized Phosphinidenes Exhibiting Strong Intramolecular Charge Transfer Transition

The unstable species dichlorosilylene was previously stabilized by carbene. The lone pair of electrons on the silicon atom of (carbene)­SiCl₂ can form a coordinate bond with metal–carbonyls. Herein we report that (carbene)­SiCl₂ can stabilize a phosphinidene (Ar–P, a carbone analogue) with the general formula carbene→SiCl₂→P–Ar (carbene = cyclic alkyl­(amino) carbene (cAAC; <b>2</b>) and N-heterocyclic carbene (NHC; <b>3</b>)). Compounds <b>2</b> and <b>3</b> are stable, isolable, and storable at 0 °C (<b>2</b>) to room temperature (<b>3</b>) under an inert atmosphere. The crystals of <b>2</b> and <b>3</b> are dark blue and red, respectively. The intense blue color of <b>2</b> arises due to the strong intramolecular charge transfer (ICT) transition from π_SiP→π*_cAAC. The electronic structure and bonding of <b>2</b>, <b>3</b> were studied by theoretical calculations. The HOMO of the molecule is located on the π_SiP bond, while the LUMO is located at the carbene moiety (cAAC or NHC). The dramatic change in color of these compounds from red (<b>3</b>, NHC) to blue (<b>2</b>, cAAC) is ascribed to the difference in energy of the LUMO within the carbenes (cAAC/NHC) due to a lower lying LUMO of cAAC

Approaches to Sigma Complexes via Displacement of Agostic Interactions: An Experimental and Theoretical Investigation

A series of coordinatively unsaturated, 16-electron, cationic ruthenium complexes bearing PNP pincer ligands of the type [RuH­(L)­(PN^RP)]⁺ (L = PPh₃, R = PhCH₂ (<b>3</b>), Ph (<b>4</b>); L = CO, R = PhCH₂ (<b>5</b>); PN^RP = RN­(CH₂CH₂PPh₂)₂) has been prepared and characterized. These complexes exhibit agostic interaction in the sixth coordination site. The binding of various X–H (X = H, Si, B, and C) bonds in small molecules such as H₂, silanes, tetracoordinate boranes, and CH₄ to the ruthenium center via displacement of the relatively weak agostic interaction in these complexes has been studied. Structures of [RuH­(L)­(PN^RP)]⁺ (L = PPh₃, R = PhCH₂ (<b>3</b>), Ph (<b>4</b>); L = CO, R = PhCH₂ (<b>5</b>); PN^RP = RN­(CH₂CH₂PPh₂)₂) complexes and the sigma-borane complex <i>trans</i>-[RuH­(CO)­(η¹-H-BH₂·NMe₃)­(PN^RP)]⁺ (R = PhCH₂ (<b>15</b>)) have been established by X-ray crystallography. The relative binding strengths of the X–H bonds to ruthenium center in these complexes has been studied using computational methods

En Route to a Molecular Terminal Tin Oxide

In the pursuit of terminal tin chalcogenides, heteroleptic stannylenes bearing terphenyl- and hexamethyldisilazide ligands were reacted with carbodiimides to yield the respective guanidinato complexes. Further supported by quantum chemical calculations, this revealed that the iso-propyl-substituted derivative provides the maximum steric protection achievable. Oxidation with elemental selenium produced monomeric terminal tin selenides with four-coordinate tin centers. In reactions with N2O as oxygen transfer reagent, silyl migration toward putative terminal tin oxide intermediates gave rise to tin complexes with terminal OSiMe3 functionality. To prevent silyl migration, the silyl groups were substituted with cyclohexyl moieties. This analogue exhibited distinctively different reactivities toward selenium and N2O, yielding a 1,2,3,4,5-tetraselenastannolane and chalcogenide-bridged dimeric compounds, respectively