Pressure‐Enhanced C–H Bond Activation in Chloromethane Platinum(II) Complexes

Abstract

The nature of the interaction between chloromethanes CH 4-n Cl n and Pt(II) complexes has been studied by highpressure X-ray diffraction and infrared spectroscopy in combination with DFT calculations. In case of electron rich complexes such as d 8 -Pt(btz-N,N′)(phenyl)L with L = phenyl, Cl, Br and btz = 2,2′-Bi-5,6-dihydro-4H-1,3-thiazine stable chloroform adducts with bridging hydrogen atoms in the η 1 (C-H)Pt moieties were isolated which display highly activated C-H bonds. This activa-The activation of carbon-hydrogen bonds is usually hampered by their rather apolar covalent character and large bond dissociation energies. For example the C-H bond dissociation enthalpies in simple alkanes such as methane [DH 298 = 439.28(13) kJ mol -1 ] are virtually as large as in the H 2 molecule [DH 298 = 435.998(13) kJ mol -1 ] displaying the prototype of a strong covalent bond. [1] As a consequence, alkanes are neither good electron donors nor good acceptors since the σ(C-H) bonding orbital is low in energy while the antibonding σ*(C-H) orbital is high lying. Hence, C-H bonds are generally considered to be chemically rather inert and their selective activation remains a challenge in organometallic chemistry. [2][3][4] This obstacle can be overcome by metal-assisted C-H bond activation in cases where an alkane ligand coordinates either end-on (η 1 ) or side-on (η 2 ) to a metal-ligand fragment ML n (Scheme 1). [5,6] In case of electron-rich late transition metal complexes two bonding scenarios with short M···H br -C contacts are usually observed for methane and halomethane d 8 -Pt complexes, where H br denotes a bridging hydrogen atom. These are illustrated in case of the theoretical model systems (CH 3 ) 2 Pt(NH 3 )(CH 4 ) 1a and (CH 3 ) 2 Pt(NH 3 ) 2 ·(CHCl 3 ) 1b in Scheme 1. We note, that all DFT calculations were performed with ADF using the BP86 functional, the ZORA for the descrip- [a]

Ortho-aryl substituted DPEphos ligands: rhodium complexes featuring C–H anagostic interactions and B–H agostic bonds

“…Such demarcations are not always clear-cut, however, as axial sites can also display Lewis-acidic character. 29,41 While with hindsight it is not surprising that the most sterically bulky ligand, DPEphos-i Pr, enforces an anagostic interaction at room temperature, the presence of both aryl and, rarer, 42,43 alkyl anagostic interactions in 2-Me is perhaps more notable. What was unanticipated is that in the parent DPEphos-H complex such interactions are also present -albeit only observed at very low temperature in solution.…”

BODIPY–dipicolylamine complexes of platinum(ii): X-ray structure, cellular imaging and organelle-specific near-IR light type-II PDT

“…Potassium tetrachloroplatinate (K 2 PtCl 4 ) was procured from Arora Matthey (India) and converted to [Pt(DMSO) 2 Cl 2 ] as a precursor. 50 The 1 H and 13 C NMR spectra were recorded using a Bruker Avance 400 MHz NMR spectrometer at 298 K and tetramethylsilane (TMS) was used as the standard. Electrospray ionization mass spectrometric (ESI-MS) data were obtained using an Agilent 6538 ultra high definition (UHD) accurate-mass quadrupole time-of-flight (Q-TOF) instrument.…”

Ultrafast Vibrational Response of Activated C–D Bonds in a Chloroform–Platinum(II) Complex

“…The latter can establish a non-classical M···H–C metal hydrogen bond between the metal ligand fragment and the C–H bond of the chloroform ligand. 9 …”

“…We note that the red shift of a C–H band can be used to characterize metal-induced bond activation as a result of agostic or M···H–C hydrogen bonding in solution. 9 , 13 , 14 …”

“…This is mainly due to the predominant Pt(d z 2 ) → σ*(C–D) back donation and a secondary Pt(RY) ← σ(C–H) donation into unoccupied extravalent (“Rydberg”) d orbitals at the metal as revealed by second-order perturbation theory natural bond orbital (NBO) analysis. 9 , 19 The Pt(d z 2 ) → σ*(C–D) interaction amounts to −26.3 kJ mol –1 and provides a substantial contribution to the total bonding energy between the metal ligand fragment and the chloroform ligand (−64.6 kJ mol –1 ) as derived by an energy decomposition analysis (EDA). 20 …”