Reaction of L2Zn2 with Ph2E 2-synthesis of LZnEPh and reactions with oxygen and H-acidic substrates

Article abstract of DOI:10.1039/c3cc48677j

L₂Zn₂ (L = HC[C(Me)N(2,4,6-Me₃C ₆H₂)]₂) and Ph₂E₂ (E = Se, Te) react to form LZnSePh (1) and LZnTePh (2). 1 and 2 further react with H₂O and EtOH to form LZ

Full text of DOI:10.1039/c3cc48677j

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Reaction of L2Zn2 with Ph2E2 – synthesis of
LZnEPh and reactions with oxygen and
H-acidic substrates†‡
Cite this: Chem. Commun., 2014,
50, 1189
Received 13th November 2013,
Accepted 15th November 2013
S. Gondzik, S. Schulz,* D. Blaser and C. Wolper
¨
¨
DOI: 10.1039/c3cc48677j
www.rsc.org/chemcomm
L2Zn2 (L = HC[C(Me)N(2,4,6-Me3C6H2)]2) and Ph2E2 (E = Se, Te) react of L2Zn2 with Ph2E2 (E = Se, Te), yielding LZnEPh (E = Se 1, Te 2).
to form LZnSePh (1) and LZnTePh (2). 1 and 2 further react with H2O Moreover, reactions of 1 and 2 with H-acidic substrates and O2
and EtOH to form LZnOH (3) and LZnOEt (4), respectively, whereas (2) are reported.
the reaction of 2 with oxygen yielded [LZnOTe(O)Ph]2 (5). 1, 4 and 5
were characterized by single crystal X-ray diffraction.
Insertion reactions of chalcogen atoms into the Zn–Zn bond
of univalent Zn(I) complexes by reaction with elemental chalco-
genes E or chalcogenophosphoranes Bu3PQE (E = Se, Te)
The discovery of [Z5-Cp*2Zn2],1 the first organozinc(I) complex failed. In contrast, reactions of L2Zn2 with one equivalent of
with a zinc–zinc bond, has boosted research activities on Ph2E2 gave the zinc chalcogenide complexes LZnEPh (E = Se 1,
univalent zinc complexes. Since then, almost 25 Zn(I) com- Te 2, Scheme 1). 1 and 2 were characterized by 1H and 13C NMR
plexes have been structurally characterized and their chemical spectroscopy. The spectra showed the resonances due to the
reactivity has been investigated.2 Reactions with Lewis bases b-diketiminato and the Ph group in a relative intensity of 1 : 1.
and H-acidic compounds were found to proceed with preserva- The resonances of the b-diketiminato group are slightly shifted
tion of the Zn–Zn bond,3 and reactions with transition metal compared to those of the starting Zn(I) complex. The 125Te NMR
complexes demonstrated the capability of Cp*Zn and Cp*Zn2 to spectrum of 2 shows a resonance at 416 ppm as is typical for
stabilize transition metal complexes.4 In addition, the electro- Te(II) compounds.13 Recently, reactions of R2E2 with RSnSnR
chemical behavior of Cp*2Zn2 was studied by CV,5 and the and intramolecularly stabilized Sb(I) and Bi(I) complexes were
capability of Cp*2Zn2 to serve as a pre-catalyst for inter- reported to proceed with E–E-bond cleavage.14
molecular hydroamination reactions was shown.6
X-ray quality crystals of 1 were obtained from a solution in
Surprisingly, selective insertion reactions into the Zn–Zn fluorobenzene upon storage at 4 1C for 12 h (Fig. 1). 1 crystal-
bond and reactions in which Zn(I) complexes serve as reducing lizes in the monoclinic space group P21/n with two molecules in
agents comparable to Mg(I) complexes7,8 are almost unknown. the elemental cell. The molecule is located on a center of
Only the reaction of an a-diimine stabilized Zn(I) complex with inversion. The six-membered C3N2Zn rings are almost planar
PhCCH, which occurred with H2 elimination,9 and oxidative (deviation of Zn from the least-squares plane of the ligand
addition reactions of a Zn(I) complex with alkyl halides, yield- 0.6013(19) Å, r.m.s. deviation of the ligand atoms from the
ing 1 : 1 mixtures of ZnR2 and ZnX2, were reported.10 Due to plane 0.0447 Å) and the average C–C (1.410(2) Å), C–N (1.330(4) Å)
our long-term interest in the reactivity of low-valent organo- and Zn–N (1.973(7) Å) bond lengths are almost identical to
metallic complexes,11 we recently investigated reactions of L2Zn2 those in L2Zn2.15 The Zn–Se bonds of 2.4291(5) and 2.5951(6) Å
(L = HC[C(Me)N(2,4,6-Me3C6H2)]2) with group 14 azides, yielding are within the typical range observed for Zn–Se bonds with
the first zinc hexazene complex.12 We now report on the reaction
¨
University of Duisburg-Essen, Universitatsstr. 5-7, S07 S03 C30, 45117 Essen,
Germany. E-mail: stephan.schulz@uni-due.de; Fax: +49 201 1833830;
Tel: +49 201 1834635
† Dedicated to Prof. Edgar Niecke on the occasion of his 75th birthday.
‡ Electronic supplementary information (ESI) available: Experimental procedures
and characterization of 1–5. CCDC 970723 (1), CCDC 964285 (4) and CCDC
964286 (5). For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3cc48677j
Scheme 1 Synthesis of 1 and 2.
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Fig. 2 Solid state structure of 5; the inversion center in the ring center.
Labelled non-H-atoms of the asymmetric unit and symmetry-generated
(ꢀx + 1,ꢀy + 2,ꢀz + 1) atoms shown as thermal ellipsoids (50% probability
levels); H atoms omitted for clarity.
Fig. 1 Solid state structure of 1; the inversion center in the ring center.
Labelled non-H-atoms of the asymmetric unit and symmetry-generated
(ꢀx + 1,ꢀy,ꢀz + 2) atoms shown as thermal ellipsoids (50% probability
levels); H atoms omitted for clarity.
each of them disordered over two positions, in the unit cell and
adopts a dimeric structure with a crystallographic inversion
center that renders the two halves of the molecule equivalent.
The Zn atoms in 5 are slightly out of the plane of the six-
membered C3N2Zn rings (deviation from the least-squares
plane of the ligand 0.213(2) Å, r.m.s. deviation of the ligand
atoms from the plane 0.0248 Å) and the average C–C (1.407 Å)
and C–N (1.326 Å) bond lengths as well as Zn–N (Zn1–N1 1.9620
(14), Zn1–N2 1.9589(14) Å) bond lengths within the C3N2Zn ring
are almost identical to those in L2Zn2.15 The average Zn–O bond
lengths (Zn1–O1 1.9678(13), Zn1–O2 1.9553(13) Å) within the
envelope-type eight-membered Zn2Te2O4 ring are also within
the typical range observed for Zn(II) alkoxides.18
The Te–O bonds (Te1–O1 1.8524(13), Te1–O2A 1.8529 (12) Å)
compare well to the mean value (1.913(46) Å) for this substruc-
ture fragment as derived from a CSD search.19 The bond order
within tellurinates can be described as 1.5, hence their Te–O
bond lengths are typically shorter compared to Te–O single
bonds (roughly 2 Å). The endocyclic O1–Te1–O20 bond angle
(98.79(6)1) is slightly smaller compared to the endocyclic
O1–Zn1–O2 (102.67(6)1) bond angle. The C–Te–O bond angles
(O1–Te1–C24 97.71(7)1, O20–Te1–C24 95.70(6)1) indicate a high
p-character of the bonding electron pairs as is typical for the
heaviest main group elements (Fig. 3).
fourfold-coordinated Zn and threefold-coordinated Se atoms.16
The endocyclic Se–Zn–Se bond angle (89.003(14)1) is slightly
smaller than the Zn–Se–Zn bond angle (90.997(14)1).
Since X-ray quality crystals of 2 could not be obtained, we
investigated reactions of 1 and 2 with H-acidic substrates.
Treatment of 1 with water and ethanol proceeded with forma-
tion of PhSeH, which was identified by its 77Se NMR spectrum
(ESI‡), as well as LZnOH (3) and LZnOEt (4), which were
identified by NMR spectroscopy and by single crystal X-ray
analysis (4).17 Reaction of 2 with water and ethanol gave a
dark-red solution, from which 3 and 4 could also be isolated.
However, 125Te NMR spectroscopy studies did not reveal the
formation of PhTeH (ESI‡). Instead, a new resonance at 3210 ppm
most likely indicates the formation of the [Te4]2+ dication.
Finally, the reaction of 2 with O2 was investigated, yielding 5.
1
The H and 13C NMR resonances of the b-diketiminato and the
Ph group of 5 are slightly shifted compared to those of 2. The
125Te NMR spectrum of 5 shows a resonance at 1681 ppm, which
is shifted to lower field as is typical for telluroxanes (Scheme 2).13
Colourless crystals of 5 were obtained upon storage of a
solution of 5 in fluorobenzene at 18 1C (Fig. 2). 5 crystallizes in
the monoclinic space group P21/c with four C6H5F molecules,
5 represents a rare example of a metalated tellurinic acid
(RTe(O)OH). Aryltellurinic(IV) acids [RTe(O)(OH)]n, typically pre-
pared by base hydrolysis of tellurium trichlorides RTeCl3, and
their corresponding anhydrides [RTeO1.5]n are mostly ill-defined,
amorphous substances. Only very recently, well-defined molec-
ular tellurinic acids and oligomeric tellurinic anhydrides were
reported.20–22 The sodium salts of both acids20,23 and two
stannatellurinates RTeO2Sn(Cl)t-Bu2 (R
= 2,4,6-t-Bu3C6H2,
8-Me2NC10H6) were also structurally characterized.24
Scheme 2 Synthesis of 5.
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