Structural Basis for Unusually Long Wavelength Charge Transfer Transitions in Complexes [MCl(ECH₂CH₂NMe₂)(PR₃)] (E = Te, Se; M = Pt, Pd):  Experimental Results and TD-DFT Calculations

Abstract

A series of new complexes, the blue compounds [PdCl(TeCH(2)CH(2)NMe(2))(PR(3))] (PR(3) = PEt(3), PPr(n)(3), PBu(n)(3), PMe(2)Ph, PMePh(2), PPh(3), PTol(3)) and the red [PtCl(TeCH(2)CH(2)NMe(2))(PR(3))] (PR(3) = PMe(2)Ph, PMePh(2)), were synthesized and studied spectroscopically ((1)H and (31)P NMR, UV/vis) and by cyclic voltammetry. The structures of [PdCl(TeCH(2)CH(2)NMe(2))(PPr(n)(3))] (2b) [PdCl(TeCH(2)CH(2)NMe(2))(PMePh(2))] (2e), [PtCl(TeCH(2)CH(2)NMe(2))(PMePh(2))] (2i), and the related [PtCl(SeCH(2)CH(2)NMe(2))(PEt(3))] (3) were determined crystallographically, revealing a typical pattern of trans-positioned neutral N and P donor atoms in an approximately square planar setting. The molecules 2b, 2e, and 2i were calculated by TD-DFT methodology to understand the origin of the weak (epsilon approximately 200 M(-1) cm(-1)) long-wavelength bands at about 600 nm for Pd/Te complexes such as 2b or 2e, at ca. 460 nm for Pt/Te systems such as 2i, and at about 405 nm for Pt/Se analogues such as 3. These transitions are identified as charge transfer transitions from the selenolato or tellurolato centers to unoccupied orbitals involving mainly the phosphine coligands for the Pt(II) compounds and more delocalized MOs for the Pd(II) analogues. Calculations and electrochemical data were used to rationalize the effects of metal and chalcogen variation.

Interconversion of structurally characterised complexes [PdCl(Se ̂ N)] 2 and [Pd(Se ̂ N) 2 ] 6 with the hemi-labile ligand Se ̂ N=Me 2 NCH 2 CH 2 CH 2 Se −

“…The PdÁ Á ÁPd distances of 3.1528(15) and 3.2289 (15) A are shorter than the sum of the van der Waals radii for two Pd atoms (3.26 A) [16]. A view on the above mentioned complexes reveals that the PdÁ Á ÁPd distances range from very short 3.105 (2) A for [(l-SePh) 2 {PdCl 2 } 2 ] 2À [13] to 3.681 (2) A in [Pd 2 (l-SePh) 2 (SePh) 2 (PPh 3 ) 2 ] [15], implying that the PdÁ Á ÁPd distance is governed by the Pd-Se bond lengths and angles in the Pd(l-SeR) 2 Pd framework.…”

“…As a consequence of the formation of a Pd 2 Se 12 ''hexagon'' the Se-Pd-Se angles around an individual Pd atom are split into sets of more obtuse (parallel to the ring axis, around 98°) and sharpened (within the ring plane, around 82°) angles. The average Pd-Se bond length of 2.437 A lies in the range of related complexes with Pd(l-SeR) 2 Pd frameworks such as [Pd 2 Cl 2 (lSeCH 2 CH 2 CH 2 NMe 2 ) 2 ] (2.3858(7) and 2.4037 (7) A [9]) and [Pd 2 (l-SePh) 2 (SePh) 2 (PPh 3 ) 2 ] (2.464 (2) and 2.494 (2) A) [15]. In a similar compound [(l-SePh) 2 (6) A) [1].…”

“…The average Pd-Se bond length of 2.437 A lies in the range of related complexes with Pd(l-SeR) 2 Pd frameworks such as [Pd 2 Cl 2 (lSeCH 2 CH 2 CH 2 NMe 2 ) 2 ] (2.3858(7) and 2.4037 (7) A [9]) and [Pd 2 (l-SePh) 2 (SePh) 2 (PPh 3 ) 2 ] (2.464 (2) and 2.494 (2) A) [15]. In a similar compound [(l-SePh) 2 (6) A) [1]. The PdÁ Á ÁPd distances of 3.1528(15) and 3.2289 (15) A are shorter than the sum of the van der Waals radii for two Pd atoms (3.26 A) [16].…”

“…These include the search for molecular precursors for the synthesis of metal chalcogenides [1], the study of metal mediated donor-acceptor interactions between coordinated ligands [2], and versatile coordination chemistry. Internal functionalisation through the N donor provides a way to suppress polymerisation of metal chalcogenolates [3].…”

“…Internal functionalisation through the N donor provides a way to suppress polymerisation of metal chalcogenolates [3]. While the chemistry of mercaptoalkylamines is now fairly well explored [4][5][6], the heavier analogs containing Se or Te have been investigated only recently [1,2,[7][8][9].…”