Aryldiazenido complexes: structure, fluxionality, and properties of the iridium ethylene aryldiazenido complex [(η5-C5Me5)Ir(C2H4)(p-N2C6H4OMe)][BF4] and a comparison with the analogous nitrosyl complex [(η5-C5Me5)Ir(C2H4)(NO)][BF4]
Abstract:[Cp*Ir(C2H4)(N2Ar)][BF4] (1BF4; Ar = p-N2C6H4OMe) has been synthesized by reacting [ArN2] [BF4] with Cp*Ir(C2H4)2 at low temperature. An initial electrophilic attack of the incoming diazonium ion at iridium, followed by expulsion of C2H4, is postulated to account for the mild reaction conditions that are in sharp contrast to the usual inertness of the bis(ethylene) compound toward ligand substitution. The IR and nitrogen NMR data for 1BF4 and its 15Nα derivative unambiguously establish that the ArN2 ligand has… Show more
“…[24,25] In these cases, Au III species bearing an aryldiazenide ligand (ArN 2 À )h ave been proposed as the key intermediates that undergo the photoelimination of N 2 ,b ut they were not isolated. Arenediazoniums are also known to oxidatively add to complexes of several metal ions, including Ru II , [30] Ir I [31] or Pd II , [32] to give aryldiazenidec omplexes. As far as we are aware,t here is only one report describing the oxidative addition of an arenediazonium to aP t II species, which gives al abile aryldiazenide Pt IV complex that easily undergoes N 2 elimination.…”
A stereoselective synthetic route to homo‐ and heteroleptic facial tris‐cyclometalated PtIV complexes is reported, involving the oxidative addition of 2‐(2‐pyridyl)‐ or 2‐(1‐isoquinolinyl)benzenediazonium salts to cis‐[Pt(C^N)2] precursors, with C^N=cyclometalated 2‐(p‐tolyl)pyridine (tpy), 2‐phenylquinoline (pq), 2‐(2‐thienyl)pyridine or 1‐phenylisoquinoline (piq), to produce labile diazenide intermediates that undergo photochemical or thermal elimination of N2. The method allows the preparation of derivatives bearing cyclometalated ligands of low π–π* transition energies. The new complexes exhibit phosphorescence in fluid solution at room temperature arising from triplet ligand‐centered (3LC) excited states, which, in the cases of the heteroleptic derivatives, involve the ligand with the lowest π–π* gap. The heteroleptic piq derivatives exhibit fluorescence and dual phosphorescence from different ligand‐centered excited states in rigid media, demonstrating the potential of cyclometalated PtIV complexes as multi‐emissive materials.
“…[24,25] In these cases, Au III species bearing an aryldiazenide ligand (ArN 2 À )h ave been proposed as the key intermediates that undergo the photoelimination of N 2 ,b ut they were not isolated. Arenediazoniums are also known to oxidatively add to complexes of several metal ions, including Ru II , [30] Ir I [31] or Pd II , [32] to give aryldiazenidec omplexes. As far as we are aware,t here is only one report describing the oxidative addition of an arenediazonium to aP t II species, which gives al abile aryldiazenide Pt IV complex that easily undergoes N 2 elimination.…”
A stereoselective synthetic route to homo‐ and heteroleptic facial tris‐cyclometalated PtIV complexes is reported, involving the oxidative addition of 2‐(2‐pyridyl)‐ or 2‐(1‐isoquinolinyl)benzenediazonium salts to cis‐[Pt(C^N)2] precursors, with C^N=cyclometalated 2‐(p‐tolyl)pyridine (tpy), 2‐phenylquinoline (pq), 2‐(2‐thienyl)pyridine or 1‐phenylisoquinoline (piq), to produce labile diazenide intermediates that undergo photochemical or thermal elimination of N2. The method allows the preparation of derivatives bearing cyclometalated ligands of low π–π* transition energies. The new complexes exhibit phosphorescence in fluid solution at room temperature arising from triplet ligand‐centered (3LC) excited states, which, in the cases of the heteroleptic derivatives, involve the ligand with the lowest π–π* gap. The heteroleptic piq derivatives exhibit fluorescence and dual phosphorescence from different ligand‐centered excited states in rigid media, demonstrating the potential of cyclometalated PtIV complexes as multi‐emissive materials.
“…In an earlier paper of this series we reported that the singly-bent aryldiazenido ligand , bound in an end-on coordination fashion ( I ), has unique anisotropic π electronic properties 4a. It has strong π-accepting ability only in the bending plane, whereas in the perpendicular direction it is a moderate π-donor.…”
Section: Introductionmentioning
confidence: 99%
“…Of key importance is an understanding of the geometric and electronic requirements of the differently coordinated aryldiazenido ligands in complexes. Some effort has been made to obtain a general theoretical description of the electronic structure of the bonding in transition metal organodiazenido complexes. − 4a However, little is known about how the molecular geometry, the properties of ancillary ligands, or, importantly, the geometrical disposition of the ancillary ligand in a given molecular geometry influence the metal−aryldiazenido bonding. We have been concerned with these questions, both in the experimental arena and in the theoretical domain.…”
The complex
[(η5-C5Me5)Ir(C2H4)(p-N2C6H4OMe)][BF4]
(1) reacts with X- = I- and
Br- to give neutral [(η5-C5Me5)IrX]2(μ-η2-p-N2C6H4OMe)(μ-η1-p-N2C6H4OMe)
where X = I (2) and Br (3), respectively.
The
spectroscopic data for 2 and 3, as well as their
15Nα derivatives 2a and
3a, establish that 2 and 3 are
isostructural
in solution and each contains diiridium centers that are bridged by two
coordinatively different aryldiazenido
ligands, i.e., μ-η2- and
μ-η1-p-N2C6H4OMe
groups. This structural feature has also been unequivocally
confirmed
in the solid state by a single-crystal X-ray crystallographic analysis
of 2. The NMR studies of the protonation
reactions of 2a and 3a indicate that protonation
occurs solely at the Nα atom of the
μ-η2-p-N2C6H4OMe
ligand
in both cases. When 1 reacts with the metal base
complex
(η5-C5Me5)Ir(CO)2
in ethanol at reflux, the monobridging
aryldiazenido complex
[{(η5-C5Me5)Ir(CO)}2(μ-η2-p-N2C6H4OMe)][BF4]
(6) results. The molecular structure of
6 in the solid state, established by a single-crystal X-ray
crystallographic analysis, is consistent with its
spectroscopic
properties in solution. On the basis of an EHMO calculation and a
fragment orbital interaction analysis, a rationale
is suggested to explain how the electronic nature of the substituent
ligand influences the outcome of substitution
reactions of 1. Complex 2 crystallized in
the space group P1̄ with a = 8.937(2)
Å, b = 10.036(2) Å, c =
10.893(2) Å, α = 79.98(1)°, β = 79.52(1)°,
γ = 70.36(1)°, and Z = 1. The structure of
2 was refined to R
F
=
0.021 and R
w
F
= 0.029
on the basis of 3077 observed independent reflections with
I
o ≥ 2.5σ(I
o) and
189 variables
in the range 2θ = 4−52°. Complex 6 crystallized
in the space group Pc21
b with
a = 8.821(1) Å, b =
20.237(2)
Å, c = 34.808(5) Å, and Z = 8.
The structure of 6 was refined to
R
F
= 0.044 and
R
w
F
= 0.049 on the
basis of
1661 observed independent reflections with I
o ≥
2.5σ(I
o) and 259 variables in the range
2θ = 4−50°.
“…Thus, the aryl ring may, in principle, be directed syn to either of the ligands L 1 or L 2 . Furthermore, when the ligands L 1 and L 2 differ in their π donor−acceptor properties, the d orbital is rotated and the plane of the aryldiazenido ligand therefore is also rotated, so that now the CN···ReL 1 dihedral angle is near 90° (where L 1 is the better π acceptor) as in Scheme . , 1 (a) Idealized Conformers of [Cp*ReL 1 L 2 (N 2 Ar)] + That Arise from the Two Possible Orientations of the Aryldiazenido Ligand. (b) Diagram To Show the Important Overlap of the Filled Rhenium d π Orbital with the Empty In-Plane Nitrogen p Orbital …”
The variable temperature 1 H NMR spectra of Cp*ReH(CO)(p-N 2 C 6 H 4 OMe) (1) and Cp*Re-(CH 3 )(CO)(p-N 2 C 6 H 4 OMe) (3) and the variable temperature 31 P{ 1 H} NMR spectra of Cp*ReCl-(PR 3 )(p-N 2 C 6 H 4 OMe) [R ) Me (4), OMe (5), Ph (7)] are presented and discussed. The spectra of 1 and 3-5 show that at low temperature two isomers are present in each case and that these isomers interconvert on the NMR time scale. The isomers are interpreted to occur because the p-N 2 C 6 H 4 OMe ligand adopts two different orientations where the aryl group is oriented syn to either the X or Y ligand in these chiral complexes of general formula Cp*ReXY(p-N 2 C 6 H 4 OMe). The bulky PPh 3 ligand in 7 results in an overwhelming preference for orientation only syn to the Cl group and thus only one observable isomer. The activation parameters for the conformational isomerization of the aryldiazenido ligand in these neutral complexes have been obtained from NMR line shape analyses and are compared with data obtained previously for related cationic rhenium aryldiazenido complexes.
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