Synthesis and characterization of 4,4′-methylenebis (2,6-di-tert-butylphenol) derivatives of a series of metal alkoxides and alkyls

Article abstract of DOI:10.1080/00958972.2012.654785

Investigation of the coordination behavior of 4,4′-methylenebis(2,6- di-tert-butylphenol) (or H₂-4DBP) with a series of metal alkoxides led to isolation of [(OR)₃M]₂(μ-4DBP), where M/OR=Ti/OBu^t (2), Ti/ONep (3),

Full text of DOI:10.1080/00958972.2012.654785

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Synthesis and characterization of
4,4′-methylenebis (2,6-di-tert-
butylphenol) derivatives of a series of
metal alkoxides and alkyls
Timothy J. Boyle a , Leigh Anna M. Steele a & Daniel T. Yonemoto a
a Sandia National Laboratories, Advanced Materials Laboratory ,
1001 University Boulevard, SE , Albuquerque , NM 87106 , USA
Published online: 30 Jan 2012.
To cite this article: Timothy J. Boyle , Leigh Anna M. Steele & Daniel T. Yonemoto (2012)
Synthesis and characterization of 4,4′-methylenebis (2,6-di-tert-butylphenol) derivatives of
a series of metal alkoxides and alkyls, Journal of Coordination Chemistry, 65:3, 487-505, DOI:
10.1080/00958972.2012.654785
To link to this article: http://dx.doi.org/10.1080/00958972.2012.654785
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Journal of Coordination Chemistry
Vol. 65, No. 3, 10 February 2012, 487–505
Synthesis and characterization of 4,49-methylenebis
(2,6-di-tert-butylphenol) derivatives of a series of
metal alkoxides and alkyls
TIMOTHY J. BOYLE*, LEIGH ANNA M. STEELE and
DANIEL T. YONEMOTO
Sandia National Laboratories, Advanced Materials Laboratory,
1001 University Boulevard, SE, Albuquerque, NM 87106, USA
(Received 27 October 2011; in final form 6 December 2011)
Investigation of the coordination behavior of 4,40-methylenebis(2,6-di-tert-butylphenol) (or H2-
4DBP) with a series of metal alkoxides led to isolation of [(OR)3M]2(m-4DBP), where
M/OR ¼ Ti/OBut (2), Ti/ONep (3), Zr/OBut (4), Hf/OBut (5), and [(py)(OR)3M]2(m-4DBP) ꢀ py
(5a), where py ¼ pyridine and ONep ¼ OCH2C(CH3)3. Metal alkyl derivatives of 4DBP were
also studied and found to form similar di-substituted species: [(py)2(Et)Zn]2(m-4DBP) ꢀ py (6),
[(THF)3(Br)Mg]2(m-4DBP) (7), [(THF)2(Br)Mg](m-4DBP)[Mg(Br)(THF)3] ꢀ (THF, tol) (7a),
and [(py)(R)2Al]2(m-4DBP), where R ¼ CH3 (8), Et (9), CH2CH(CH3)2 (10); tol ¼ toluene and
THF ¼ tetrahydrofuran. All structures demonstrate the bridging nature of 4DBP and the
ability to bind a variety of metal centers. Solution state NMR indicates that the structures of 2–
10 are retained in solution. Thermal analyses indicate that 4DBP is preferentially lost during
heating.
Keywords: Metal alkoxides; Bidentate phenoxides; Group 4; Aluminum; Zinc; Magnesium
1. Introduction
Metal alkoxides [M(OR)x] have found widespread utility as precursors to ceramic oxide
materials in bulk powder, thin film, or nanomaterial form. In many instances, the
nuclearity of the M(OR)x precursor has been shown to play a role in determining the
various properties of the final ceramic [1–13]; therefore, it is of interest to garner control
over the structure of these precursors. Unfortunately, due to the large cation size and
small charge of the ligands, M(OR)x often suffer from clustering and oligomerization
with bridging alkoxide (m-OR) ligands filling open coordination sites. We have
demonstrated some control of the assembly of Ti(OR)4 using select ligands, such as
dihydroxypyridimine (H2-DHP) [14] and pyridine carbinol (H–OPy) [15] shown in
figure 1(a) and (b). Previously, the DHP ligand was found to act solely as a bridging
ligand between ‘‘Ti(OR)3’’ moieties but the solubility of the resulting complex was
significantly reduced. For the OPy derivatives, two ligands preferentially bind bidentate
*Corresponding author. Email: tjboyle@Sandia.gov
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.654785

488
T.J. Boyle et al.
Figure 1. Schematic representation of polydentate ligands (a) dihydroxypyridimine (H2-DHP), (b) pyridine
carbinol (H-OPy), (c) 4,40-di-methoxy,2,20-di-ol-benzophenone (H2-OBzP), and (d) 4,40-methylenebis(2,6-di-
tert-butylphenol) (H2-4DBP).
to the Ti cation, thereby directing alcoholysis reactions to the remaining alkoxide
ligands [15].
Continuing our efforts to generate controlled structures of M(OR)x, we have
undertaken an investigation of polydentate aryloxide (OAr) ligands. These ligands were
of particular interest due to our previous success with aryl alcohol (phenols) [16–22] and
catechol [22] ligands in generating complex families of M(OR)x compounds. Since we
had already explored polyhydroxide aryl rings with the catechol species, it was thought
that if the aryl rings were linked, the OH positioning would facilitate control over the
final structures. This proved a valuable approach for generating dinuclear species when
using the 4,40-di-methoxy,2,20-di-ol-benzophenone (H2-OBzP) (figure 1c) [23].
For OBzP, the rigid aryl backbone and C¼O moiety led to a close interaction of two
metals [23].
For this study, the coordination behavior of the underexplored 4,40-methylenebis(2,6-
di-tert-butylphenol) (referred to as H2-4DBP or 1) ligand was undertaken.
The schematic structure of 1 is shown in figure 1(d) and a thermal plot in figure 2.
The ligand possesses more flexibility in comparison to OBzP or catecholate derivatives
and the para-OH make it of interest for controlled alcoholysis. Following equations (1)
and (2), the structural influence introduced by these ligands was determined for a series
of M(OR)x and metal alkyls (MRx), respectively.
Â
Ã
2MðORÞ4 þ H2-4DBP ꢁ! ðORÞ3M ðꢀ-4DBPÞ þ 2HOR
M ¼ Ti, Zr, Hf
2
ð1Þ

Metal alkoxides and alkyls
489
Figure 2. Structure plot of 1. Heavy atom thermal ellipsoids drawn at 30% level and carbon atoms drawn as
ball and stick for simplicity.
Â
Ã
py
2MðRÞxþH2-4DBP ꢁ! ðpyÞnðRÞxꢁ1M ðꢀ-4DBPÞ þ 2HR
2
ð2Þ
x ¼ 2: M ¼ Zn, Mg; x ¼ 3: M ¼ Al:
The products isolated were characterized by single-crystal X-ray diffraction and
identified as [(OR)3M]2(m-4DBP)], where M/OR ¼ Ti/OBut (2), Ti/ONep (3), Zr/OBut
(4), Hf/OBut (5), and [(py)(OR)3M]2(m-4DBP) ꢀ py (5a), where OBut ¼ OC(CH3)3,
ONep ¼ OCH2C(CH3)3 and py ¼ pyridine. Investigation of metal alkyl structures that
employ 4DBP led to isolation of [(py)2(Et)Zn]2(m-4DBP) ꢀ py (6, Et ¼ CH2CH3),
[(THF)3(Br)Mg]2(m-4DBP) (7), [(THF)2(Br)Mg](m-4DBP)[Mg(Br)(THF)3] ꢀ (THF,tol)
(7a), and [(py)(R)2Al]2(m-4DBP), where R ¼ CH3 (8), Et (9), CH2CH(CH3)2 (10),
tol ¼ toluene. The synthesis and characterization of these compounds and comparison
to appropriate literature compounds will be discussed.
2. Experimental
2.1. Materials and methods
All compounds described below were handled with rigorous exclusion of air and water
using standard Schlenk line and glovebox (argon) techniques. All solvents were stored
under argon and used as received (Aldrich) in Sure/SealTM bottles, including toluene,
tetrahydrofuran, and pyridine. The following chemicals were used as received (Aldrich

490
T.J. Boyle et al.
and Alfa Aesar): H2-4DBP, H–ONep, Ti(OPri)4, M(OBut)4 (M ¼ Ti, Zr, Hf), AlR3
(R ¼ Me, Et, Bui), ZnEt2 (1 M in hexanes), and (Mes)MgBr (1 M in THF).
[Ti(m-ONep)(ONep)3]2 was prepared according to literature procedures [24].
FTIR data were collected on a Nicolet 6700 FTIR spectrometer using a KBr pellet
press under a flowing nitrogen atmosphere. Elemental analysis was performed on a
Perkin-Elmer 2400 CHN-S/O Elemental Analyzer. Thermal gravimetric analyses were
conducted using a Mettler Toledo, TGA/DSC 1, STARe System under a flowing argon
atmosphere from room temperature to 650ꢂC at 5ꢂC minꢁ1. Melting points were
determined using an ElectrothermalÕ Melting Point Apparatus from room temperature
to 300ꢂC. All NMR samples were prepared from dried crystalline materials that were
handled and stored under an argon atmosphere and redissolved in toluene-d8 or
pyridine-d5.
2.2. Alkoxide general synthesis
Due to the similarity of synthesis of 2–5, a general description is supplied for this set of
compounds. One equivalent of H2-4DBP was slowly added to a stirring solution of two
equivalents of M(OR)4 dissolved in toluene (ꢃ5 mL). For each reaction the colorless
reaction mixture immediately turned bright yellow. After stirring for 12 h, if the
reaction was cloudy it was warmed slightly until all material was re-dissolved. All
solutions were left at room temperature with slow evaporation of any volatile
components, until crystals formed. Yields were not optimized and are reported for the
first batch of crystals isolated.
2.2.1. [(OBut)3Ti]2(k-4DBP) (2). Used Ti(OBut)4 (1.00 g, 2.94 mmol) and H2-4DBP
(0.624 g, 1.47 mmol). Yield: 1.29 g (46.0%). FTIR (KBr, cmꢁ1): 3068 (w), 3007 (m),
2971 (s), 2870 (s), 2707 (w), 1458 (w), 1419 (s), 1390 (w), 1361 (s), 1263 (s,sh), 1199 (s),
1124 (m), 1043 (s), 999 (s), 882 (s), 853 (w), 795 (m), 774 (w), 701 (w), 591 (m), 482(w).
1H NMR (400.1 MHz, tol-d8) ꢁ 7.23 (1.8H, s, [OC6H2(C(CH3)3)2]2CH2), 3.94 (1.0H, s,
[OC6H2(C(CH3)3)2]2CH2), 1.61 (18.3H, s, [OC6H2(C(CH3)3)2]2CH2), 1.33 (27.0H, s,
OC(CH3)3). Anal. Calcd for C53H96O8Ti2 (%): C, 66.51; H, 10.11. Found: C, 66.26;
H, 10.41.
2.2.2. [(ONep)3Ti]2(k-4DBP) (3). Used Ti(ONep)4 (0.500 g, 1.26 mmol) and H2-4DBP
(0.268 g, 0.631 mmol). Yield: 0.545 g (41.6%). FTIR (KBr, cmꢁ1): 3070 (w), 2998
(m,sh), 2954 (s), 2909 (s), 2867 (s), 2851 (s,sh), 2782 (w,sh), 2744 (w), 2698 (w), 1478 (m),
1465 (m), 1420 (s), 1394 (m), 1361 (m), 1623 (s,sh), 1246 (s), 1215 (w), 1144 (s), 1087 (s),
1
1025 (s), 935 (w), 892 (s), 864 (w,sh), 707 (s), 673 (s), 609 (w), 482 (w). H NMR
(400.1 MHz, tol-d8) ꢁ 7.27 (2H, s, [OC6H2(C(CH3)3)2]2CH2), 4.12 (6H, s, OCH2C
(CH3)3), 3.99 (0.9H, s, [OC6H2(C(CH3)3)2]2CH2), 1.63 (19H, s, [OC6H2(C(CH3)3)2]2
CH2), 0.96 (27H, s, OCH2C(CH3)3). Anal. Calcd for C59H108O8Ti2 (%): C, 68.06; H,
10.45. Found: C, 67.38; H, 10.68.
2.2.3. [(OBut)3Zr]2(k-4DBP) (4). Used Zr(OBut)4 (1.00 g, 2.60 mmol) and H2-4DBP
(0.553 g, 1.30 mmol). Yield: 1.50 g (55.4%). FTIR (KBr, cmꢁ1): 3068 (w), 2970 (s), 2926
(s,sh), 2869 (s), 1469 (m), 1422 (s), 1389 (m), 1359 (s), 1256 (s), 1232 (s), 1206 (s), 1123

Metal alkoxides and alkyls
491
(m), 1040 (s), 1001 (s), 921 (w), 894 (m), 867 (s), 786 (s), 750 (w), 697 (m), 627 (w), 595
(m), 553 (m), 486 (m). 1H NMR (400.1 MHz, tol-d8) ꢁ 7.27 (2.0H, s, [OC6H2
(C(CH3)3)2]2CH2), 4.01 (1.0H, s, [OC6H2(C(CH3)3)2]2CH2), 1.57 (16.7H, s, [OC6H2
(C(CH3)3)2]2CH2), 1.31 (27.0 H, s, OC(CH3)3). Anal. Calcd for C53H96O8Zr2 (%):
C, 60.99; H, 9.27. Found: C, 60.96; H, 9.09.
2.2.4. [(OBut)3Hf]2(k-4DBP) (5). Used Hf(OBut)4 (1.00 g, 2.12 mmol) and H2-4DBP
(0.451 g, 1.06 mmol). Yield: 1.81 g (69.9%). FTIR (KBr, cmꢁ1): 2969 (s), 2926 (m), 2869
(w), 1459 (w), 1424 (s), 1389 (w), 1361 (m), 1266 (s), 1233 (m), 1208 (s), 1188 (s), 1124
(m), 1053 (s), 1015 (s), 946 (w), 920 (w), 895 (w), 875 (m), 861 (m), 789 (m), 776 (w), 698
(w). 1H NMR (400.1 MHz, tol-d8) ꢁ 7.26 (1.7H, s, [OC6H2(C(CH3)3)2]2CH2), 4.00
(0.8H, s, [OC6H2(C(CH3)3)2]2CH2), 1.54 (17.6H, s, [OC6H2(C(CH3)3)2]2CH2), 1.31
(27.0H, s, OC(CH3)3). Anal. Calcd for C53H96Hf2O8 (%): C, 52.25; H, 7.94. Found:
C, 51.83; H, 8.14.
.
2.2.5. [(py)2(Et)Zn]2(k-4DBP) py (6). To a solution of Zn(Et)2 (4.04 mL, 4.04 mmol)
in tol (ꢃ3 mL), H2-4DBP (0.860 g, 2.02 mmol) was slowly added. After this time, a few
drops of py were added with evolution of a gas. The reaction turned from a clear
colorless solution to an orange color. After stirring for 12 h, no precipitate was observed
and crystals were isolated by slow evaporation of the volatile portion of the reaction
mixture. Yield: 1.75 g (46.9%). FTIR (KBr, cmꢁ1): 3088 (w), 3061 (m), 3002 (m), 2949
(s), 2906 (s,sh), 2857 (s), 2800 (w,sh), 1061 (m), 1485 (w), 1458 (s,sh), 1446 (s), 1415 (s),
1380 (w), 1260 (s), 1213 (s), 1150 (w), 1069 (m), 1038 (m), 1012 (w), 825 (w), 752 (w), 700
(s), 595 (w). 1H NMR (400.1 MHz, py-d5) ꢁ 8.75 (C5H5), 7.59 (C5H5), 7.51 (2.2H,
OC6H2(C(CH3)3)2]2CH2), 7.23 (C5H5), 4.21 (1.0H, s, [OC6H2(C(CH3)3)2]2CH2), 1.57
(18.1H, s, [OC6H2(C(CH3)3)2]2CH2), 1.51 (3.0H, t, CH2CH3, JH–H ¼ 8.1 Hz), 0.75
(2.0H, q, CH2CH3, JH–H ¼ 4.0 Hz). Anal. Calcd for C53H72N4O2Zn2 (%): C, 68.60;
H, 7.82; N, 6.04. Found: C, 67.76; H, 7.85; N, 5.46.
2.2.6. [(THF)3(Br)Mg]2(k-4DBP) (7). To
a solution of (Mes)MgBr (2.30 mL,
2.30 mmol) in tol/THF (ꢃ3.5 mL), H2-4DBP (0.488 g, 1.14 mmol) was slowly added.
The reaction remained colorless. After stirring for 12 h, no precipitate was observed and
crystals were isolated by slow evaporation of the volatile portion of the reaction
mixture. Yield: 0.782 g (47.1%). FTIR (KBr, cmꢁ1): 3054 (w,sh), 2995 (m,sh), 2949 (s),
2905 (s), 2868 (s), 1603 (w), 1463 (s), 1426 (s), 1382 (w), 1355 (w), 1302 (s), 1262 (m),
1200 (w), 1019 (s), 916 (w), 864 (s), 731 (m), 697 (w), 467 (w). 1H NMR (400.1 MHz, tol-
d8) ꢁ 7.40 (1.8H, [OC6H2(C(CH3)3)2]2CH2), 4.16 (0.95H, s, [OC6H2(C(CH3)3)2]2CH2),
3.61(12.7H, mult, OC4H8), 1.61 (18.0, s, [OC6H2(C(CH3)3)2]2CH2), 1.51 (3.0H, t,
CH2CH3, JH–H ¼ 8.1 Hz), 1.32 (12.8 H, mult, OC4H8). Anal. Calcd for C45H74Br2
Mg2O6 (%): C, 58.72; H, 8.11. Found: C, 58.02; H, 8.61.
2.3. AlR3 general synthesis
To a stirring mixture of the desired AlR3 in toluene, H2-4DBP was slowly added.
Effervescence was noted for each reaction and after this subsided a few drops of
pyridine were added, which also led to the evolution of a small amount of gas. The color

492
T.J. Boyle et al.
changed from a clear to pale yellow. After stirring for 12 h, the reaction mixture was set
aside to allow the volatile portion of the reaction mixture to slowly evaporate until
X-ray quality crystals formed.
2.3.1. [(py)(CH3)2Al]2(k-4DBP) (8). Used AlMe3 (0.500 g, 6.94 mmol) and H2-4DBP
(1.47 g, 3.47 mmol). Yield: 0.600 g (12.4%). FTIR (KBr, cmꢁ1): 3058 (w), 3022 (w), 2998
(w), 2954 (s), 2920 (s,sh), 2868 (s), 2705 (w), 1615 (m), 1491 (w), 1482 (w), 1462 (m),
1450 (s), 1423 (s), 1286 (s), 1273 (s,sh), 1218 (m), 1195 (m), 1157 (w), 1124 (w), 1070 (m),
1051 (m), 1019 (w), 900 (m,sh), 885 (s), 779 (w), 759 (w), 703 (s), 671 (s), 648 (m), 434
(w). 1H NMR (400.1 MHz, py-d5) ꢁ 8.73 (C5H5), 7.57 (C5H5), 7.45 (2.0H,
[OC6H2(C(CH3)3)2]2CH2), 7.20 (C5H5), 4.10 (1.1H, s, [OC6H2(C(CH3)3)2]2CH2), 1.45
(19.5H, s, [OC6H2(C(CH3)3)2]2CH2), ꢁ0.18 (6.0H, s, CH3). Anal. Calcd for
C43H64Al2N2O2 (%): C, 74.32; H, 9.28; N, 4.03. Found: C, 72.23; H, 9.03; N, 3.65.
2.3.2. [(py)(Et)2Al]2(k-4DBP) (9). Used AlEt3 (0.500 g, 4.38 mmol) and H2-4DBP
(0.931 g, 2.19 mmol). Yield: 0.712 g (21.3%). FTIR (KBr, cmꢁ1): 3067 (w), 3020 (w),
2955 (s), 2895 (s,sh), 2860 (s), 2797 (w), 2723 (w), 1615 (m), 1491 (m), 1483 (m,sh), 1450
(s), 1422 (s), 1387 (m), 1357 (m), 1283 (s), 1267 (s), 1215 (s), 1197 (m), 1158 (w), 1123
1
(w), 1070 (s), 1052 (m), 1020 (m), 977 (m,sh), 873 (s), 699 (m), 632 (m). H NMR
(400.1 MHz, py-d5) ꢁ 8.75 (C5H5), 7.60 (C5H5), 7.42 (2.0H, OC6H2(C(CH3)3)2]2CH2),
7.23 (C5H5), 4.09 (1.0H, s, [OC6H2(C(CH3)3)2]2CH2), 1.43 (17.8H, s, [OC6H2(C
(CH3)3)2]2CH2), 1.16 (5.0H, t, CH2CH3, JH–H ¼ 8.2 Hz), 0.52 (3.7 H, q, CH2CH3,
JH–H ¼ 8.1 Hz). Anal. Calcd for C47H72Al2N2O2 (%): C, 75.16; H, 9.66; N, 3.73. Found:
C, 72.42; H, 9.49; N, 3.92.
2.3.3. [(py)((CH3)2CHCH2)2Al]2(k-4DBP) (10). Used Al(Bui)3 (0.500 g, 2.52 mmol)
and H2-4DBP (0.535 g, 1.26 mmol). Yield: 0.672 g (30.8%). FTIR (KBr, cmꢁ1): 3071
(w), 3058 (w), 3019 (m), 2948 (s), 2918 (s,sh), 2886 (s,sh), 2862 (s), 2787 (w), 1613 (s),
1461(s), 1448 (s), 1421 (s), 1388 (s), 1359 (s), 1265 (s), 1215 (s), 1186 (m), 1159 (m), 1123
(m), 1068 (s), 1050 (s), 1017 (s), 941 (w), 899 (m), 871 (s), 818 (w), 781 (w), 762 (m), 702
1
(s), 667 (s), 647 (s), 439 (w). H NMR (400.1 MHz, py-d5) ꢁ 8.75 (C5H5), 7.63 (C5H5),
7.36 (2.0H, [OC6H2(C(CH3)3)2]2CH2), 7.30 (C5H5), 4.04 (0.9H, s, [OC6H2(C
(CH3)3)2]2CH2), 1.88 (1.8H, sept, CH2CH(CH3)2, JH–H ¼ 6.5 Hz), 1.42 (18.4H, s,
[OC6H2(C(CH3)3)2]2CH2), 1.03 (12.0H, d, CH2CH(CH3)2, JH–H ¼ 3.2 Hz), 0.66 (4H, d,
CH2CH(CH3)2, JH–H ¼ 2.9 Hz). Anal. Calcd for C55H88Al2N2O2 (%): C, 76.52; H,
10.27; N, 3.25. Found: C, 75.68; H, 10.20; N, 4.41.
2.4. General X-ray crystal structure information [25]
Crystals were mounted onto a glass fiber from a pool of FluorolubeTM and immediately
placed in a cold N2 vapor stream on a Bruker AXS diffractometer equipped with a
SMART 1000 CCD detector using graphite monochromated Mo-Kꢂ radiation
˚
(ꢃ ¼ 0.7107 A). Lattice determination and data collection were carried out using
SMART Version 5.054 software. Data reduction was performed using SAINTPLUS
Version 6.01 software and corrected for absorption using the SADABS program within
the SAINT software package.

Metal alkoxides and alkyls
493
Structures were solved by direct methods that yielded the heavy atoms, along with a
number of the lighter atoms or by using the PATTERSON method, which yielded the
heavy atoms. Subsequent Fourier syntheses yielded the remaining light-atom positions.
Hydrogen atoms were fixed in positions of ideal geometry and refined using APEX II
software suite software. The final refinement of each compound included anisotropic
thermal parameters for all non-hydrogen atoms. Crystal structures of M(OR)x often
contain disorder within the atoms of the ligand chain causing higher than normal final
correlations [4, 5, 26–29].
Data collection parameters for 1–10 are given in table 1. Metrical data are tabulated
in table 2. Specific issues associated with individual structures follow. Slight ligand
disorder in the pendant chains was present in 2, 3, 4, 5, 5a, 7a, and 10. Attempts to
resolve this disorder was done by applying standard crystallographic restraints using
split occupancy with residual Q-peaks. For the most part this allowed the structures to
refine to completeness and lowered the refinement values. Disordered solvent molecules
were squeezed out using the PLATON squeeze method for 4, 6, 9, and 10.
3. Results and discussion
A large number of ortho-linked Group 4 bis-phenoxide structures are available in the
literature where the ligand acts in a chelating manner due to the orientation of the
hydroxides. This arrangement is abundant for calixarene derivatives, but this family of
compounds is beyond the scope of this report. However, for three titanium chloro
derivatives with the respective 2,20-methylenebis(6-phenylphenoxy) [30] and 2,7-di-t-
butyl-9H-fluororene-1,8-diolato-O,O) [31] the ligand acted as a bridge between two
disparate metal centers. In addition, the Zr cyclopentatidenyl, chloro derivative
possessed a 3-bromo-5,50-di-t-butyl-2,20oxydiphenylmethane bridge [32]. Again, these
are not para-substituted and not alkoxide species, so comparisons may not be
representative of the behavior of alkoxy or alkyl 4DBP derivatives. There are no reports
of 4DBP derivatives for any transition metal complexes. Only two transition metals
have been reported with even the basic connectivity of this type of ligand including
(Cp*Ti)2(m-4MPhO)3, where 4MPhO ¼ 2,20-bis(4-oxyphenyl)propane) [33], and
[(HB(DMP)3)Mo(NO)(m-4MPhO)]2, where HB(DMP)3 ¼ hydrogen-tris-(3,5-dimethyl-
pyrazol-1-yl)borate [34]. Therefore, the coordination behavior of the H2-4DBP ligand
was investigated through the reaction with sets of M(OR)x and MRx.
The H2-4DBP ligand (figures 1d and 2) was of interest for several reasons: (i) the
ortho position possesses the sterically hindering t-butyl group which will assist in
minimizing oligomerization, (ii) the para linkage prevents chelation of the 4DBP ligand
to the metal upon coordination, and (iii) may act as a useful model for complexation
behavior of the plastic precursor bisphenol-A [BPA; 4,40-(propane-2,2-diyl)diphenol]
that has become of recent concern [35]. The ligand itself (1) was isolated from pyridine
and is shown in figure 2. As can be observed, the para position of the –OH moieties are
not closely associated with each other with a bend of the Ar–CH2–Ar angle of 115.4ꢂ.
This arrangement should allow for ready substitution on both reactive –OH sites, which
could lend some control.

494
T.J. Boyle et al.

Metal alkoxides and alkyls
495
ꢂ
˚
Table 2. Bond distances (A) and angles ( ) for 1–10 (L ¼ OR or R).
Angles (ꢂ)
Ar–CH2–Ar
˚
Distances (A)
Compound
Metal
M–OAr
M–L
OAr–M–L
1
2
3
4
5
5a
6
7
7a
8
–
Ti
Ti
–
–
115.4
113.7
113.7
114.4
113.2
112.9
116.1
113.5
115.2
113.5
112.9
113.3
–
1.82
1.80
1.94
1.90
1.99
1.93
1.83
1.88
1.95
1.74
1.74
1.76
1.76
1.89
1.92
1.92
1.99
2.41
2.53
1.74
1.96
1.97
110.2
108.8
110.3
110.1
112.8
129.1
119.8
135.3
117.1
114.4
111.0
Zr
Hf
Hf
Zn
Mg
Mg
Al
Al
Al
9
10
3.1. Alkoxides
Our initial investigation focused on determining the coordination behavior of the 4DBP
ligand with M(OR)x. The OBut and ONep ligands were chosen for Group 4 metals,
while the OEt or OEt/ONep species were used for Group 5 cations due to their
availability, our experience with these compounds [36–39], the steric hindrance
imparted by the existing ligand sets, and their ability to readily form crystals.
For each sample simple mixing of 4DBP with the desired M(OR)4 was undertaken in
toluene, as in equation (1). Upon mixing, each reaction turned from a clear solution to a
bright yellow color, independent of the stoichiometry investigated. For the Zr reactions,
a precipitate typically occurred which was easily redissolved upon slight warming.
Crystals were isolated by allowing the reaction to cool to room temperature, followed
by slow evaporation if necessary. The FTIR data clearly revealed that an exchange
occurred for each reaction based on the absence of the –OH stretch from the 4DBP
ligands with new M–O bends present in the fingerprint region. However, additional
information as to the exact nature of the final product was needed and single-crystal
X-ray studies were undertaken to aid in this endeavor.
For 2 and 3, the reaction proceeded as written in equation (1) yielding ‘‘Ti(OBut)3’’ or
‘‘Ti(ONep)3,’’ respectively, substitution on both –OH oxygen atoms of the 4DBP
ligand. All efforts to isolate a monosubstituted product were not successful. Attempts
with the heavier congeners led to the isolation of 4 and 5, which have similar structures
as noted for 1. The structures of 2–5 are shown in figures 3–6, respectively. The
compounds all have tetrahedrally (Td) bound metal centers with an average bend angle
of 113.6 noted for the –CH2 aryl group linker. Furthermore, crystallization of 5 from
pyridine led to coordination of a solvent molecule, yielding 5a (figure 7). This
compound possesses a coordinated py to the metal center and thus square base-
pyramidal geometry (ꢆ ¼ 0.32) with a bend angle of 112.9ꢂ. The remainder of the
distances is in line with 1–5 (table 2) or literature values of similar compounds [30–34].
Interestingly, dinuclear M(OR)x appears to be unreactive toward substitution on the
4DBP ligand. For instance, a reaction of the dimeric Group 4 compounds [H][M2(m-
ONep)3(ONep)5(OBut)] [39] (M ¼ Zr, Hf) heated at reflux in toluene with H2-4DBP

496
T.J. Boyle et al.
Figure 3. Structure plot of 2. Heavy atom thermal ellipsoids drawn at 30% level and carbon atoms drawn as
ball and stick for simplicity.
Figure 4. Structure plot of 3. Heavy atom thermal ellipsoids drawn at 30% level and carbon atoms drawn as
ball and stick for simplicity.
yielded only starting materials. Further, as Group 5 species were studied under similar
conditions, it was noted that neither [M(m-OEt)(OEt)4]2 nor [M(m-OEt)(ONep)4]2 [36,
38] (where M ¼ Nb, Ta) reacted with H2-4DBP either. The dinuclear species are
believed to be too sterically hindered to allow for the expected reaction (note: the solid

Metal alkoxides and alkyls
497
Figure 5. Structure plot of 4. Heavy atom thermal ellipsoids drawn at 30% level and carbon atoms drawn as
ball and stick for simplicity.
Figure 6. Structure plot of 5. Heavy atom thermal ellipsoids drawn at 30% level and carbon atoms drawn as
ball and stick for simplicity.
state structure of the dinuclear [Ti(m-ONep)(ONep)3]2 is reported to be monomeric in
solution [37]).
3.2. Alkyls
Further investigation of the coordination behavior of H2-4DBP was undertaken with a
series of MRx where the metal ranged from a late transition metal, to s-block to p-block
metals.

498
T.J. Boyle et al.
Figure 7. Structure plot of 5a. Heavy atom thermal ellipsoids drawn at 30% level and carbon atoms drawn
as ball and stick for simplicity. Two molecules were located in the unit cell.
Figure 8. Structure plot of 6. Heavy atom thermal ellipsoids drawn at 30% level and carbon atoms drawn as
ball and stick for simplicity.
For the late transition metal, ZnEt2 was modified by the 4DBP ligand according to
equation (2). The resulting colorless solution required the addition of pyridine to grow
X-ray quality crystals. FTIR data indicated the –OH had been removed and pyridine
was present in the final material. For 6, each –OH of the 4DBP ligand was successfully
substituted by a ‘‘ZnEt’’ moiety. In addition, two molecules of py are bound to Zn to
yield a Td geometry (figure 8). The reaction of H2-4DBP with (Mes)MgBr, where
Mes ¼ mesityl, led to isolation of an s-block metal derivative 7 (figure 9) from THF.
The FTIR data were similar to that of 6. Again, each –OH has been reacted liberating
the H-Mes by product to form a di-Mg–Br substituted 4DBP derivative. Three THF
molecules complete the distorted trigonal bipyramidal (ꢆ ¼ 0.70) coordination sphere of

Metal alkoxides and alkyls
499
Figure 9. Structure plot of 7. Heavy atom thermal ellipsoids drawn at 30% level and carbon atoms drawn as
ball and stick for simplicity.
Figure 10. Structure plot of 7a ꢀ THF,tol. Heavy atom thermal ellipsoids drawn at 30% level and carbon
atoms drawn as ball and stick for simplicity.
the Mg. From a different crystallization attempt, an interesting alternative compound
7a (figure 10) was isolated, where Mg(1) binds only one but Mg(2) binds two THF
molecules. Additionally, a THF and a toluene molecule are located in the unit cell. This
results in an asymmetrical molecule with one Mg adopting a distorted trigonal

500
T.J. Boyle et al.
Figure 11. Structure plot of 8. Heavy atom thermal ellipsoids drawn at 30% level and carbon atoms drawn
as ball and stick for simplicity.
geometry and the other forming a Td coordination. The Ar–CH2–Ar bend angles for
6–7a (table 2) were found to be consistent with each other and with 2–5a.
Finally p-block main group Al was studied (equation (2)) using AlR3 [where R¼CH3,
CH2CH3, CH2CH(CH3)2]. The reactions proceed as written, changing from colorless to
pale yellow upon addition of 4DBP. Crystals were isolated from a pyridine solution and
FTIR data collected on these compounds show the loss of –OH peak along with standard
4DBP stretches and bends. This suggests that the same substitution occurred and was
confirmed by single-crystal studies. For 8–10, similar di-substituted compounds
(see figures 11–13, respectively) were noted with each Al metal center adopting a Td
geometry by binding a py along with its parent ligands and one O from 4DBP. The bond
distances and angles of these similar species are in agreement (see table 2).
3.3. Thermal analyses
Elemental analyses of crystalline material proved to be inconsistent with the best values
reported in section 2. For M(OR)x this is often attributed to solvent loss, volatilization,
or decomposition of the precursor. However, the M(OR)4 derivatives are close to the
acceptable range, while the solvated species were not within the calculated values.
Further analyses were undertaken to understand these variations.
Melting point determinations were undertaken for each compound from room
temperature to 300ꢂC. H2-4DBP (1) was found to have a melting point of 155ꢂC and as
ꢂ
expected, upon complexation, the melting point changes [Cmpd (m.p. C)]: 2 (185), 3
(185), 4 (110), 5 (120), 8 (220), 9 (220), 10 (120). Compounds 6 and 7 did not melt in this
study. The lowering of the m.p. of 4, 5, and 10 below that of the ligand is an interesting
effect that needs to be further explored. However, the melting point data indicate that

Metal alkoxides and alkyls
501
Figure 12. Structure plot of 9. Heavy atom thermal ellipsoids drawn at 30% level and carbon atoms drawn
as ball and stick for simplicity.
Figure 13. Structure plot of 10. Heavy atom thermal ellipsoids drawn at 30% level and carbon atoms drawn
as ball and stick for simplicity.

502
T.J. Boyle et al.
Figure 14. TGA data collected under argon (5ꢂC minꢁ1 to 400ꢂC) for (a) 4, (b), 6, (c) 7, and (d) 10.
for a majority of these compounds, a preferential melt and volatilization probably occur
prior to decomposition.
Further studies on the thermal behavior were undertaken using TGA analyses of
representative species (i.e., 4, 6, 7, and 10). The weight loss associated with 4DBP was
found to initiate around 200ꢂC for each model compound. Figure 14 shows the TGA
spectra up to 400ꢂC of (a) 4, (b), 6, (c) 7, and (d) 10. For 4, the early weight loss is
consistent with loss of 4DBP along with some OBut (overall weight loss 51.4; ꢁ2 OBut,
ꢁ4DBP ¼ 51.1). For 6, the experimental weight loss of ꢁ49.3% is consistent with loss of
4DBP (ꢁ45.6%) and some pyridine moieties. For 7, the overall weight loss is consistent
with loss of ꢁ4DBP (Calcd 41.0%; exp: 38.8%). For 10, the calculated weight change of
50.6% based on loss of 4DBP was found to be consistent with experimental weight loss
of 49.8% (the early weight loss was consistent with one py). Combined these data
indicate that initiation of 4DBP loss (and other moieties necessary to maintain charge
balance) occurs at the relatively low temperature of 200ꢂC, making obtaining acceptable
elemental analyses difficult.
Interestingly, the overall weight loss (under an argon atmosphere up to 800ꢂC) was
not consistent with formation of the simple oxide. Therefore, thermal treatments of the
powders outside of the TGA instrument were performed and the resulting powders
analyzed by PXRD. The final powders for (a) 4, (b) 6, (c) 7, and (d) 10 were identified
as: (a) mixed phase of baddeleyite (PDF: 00-050-1089)/zirconium oxide (PDF: 00-050-
1089), (b) amorphous, (c) zincite (PDF: 00-005-0664), and (d) periclase (PDF: 00-004-
0829), respectively. The thermal treatment used in these experiments formed the ceramic
oxide but may not have fully converted all of the material, as evidenced by the
surprising amorphous Al derivative. Based on the low temperature melting and

Metal alkoxides and alkyls
503
preferential 4DBP loss, 1–10 are being studied as optimal precursors for metal-organic
chemical vapor deposition (MOCVD) and nanomaterial applications.
3.4. Solution behavior
To determine if the structures were retained in solution, crystals of 1–10 were
individually dissolved in a deuterated solvent at as concentrated levels as possible. The
spectra were collected at room temperature. For H2-4DBP, a simple, spectrum with
four singlets (OH, aromatic H, CH2, and But in a 1 : 2 : 1 : 18) are expected and observed
1
for the H NMR. Based on the obtained structures, upon complexation to the metals,
the symmetry should not be reduced and a similar pattern (with the loss of the –OH
peak) along with the inclusion of the resonances associated with the respective pendant
ligand chains is expected. For 1, 3, and 4 nearly identical 1H spectra were collected with
four peaks observed in a 2 : 1 : 18 : 27 ratio representing the 4DBP ligand and the OBut
of the metal. For 2, a similar spectrum as above but two ONep peaks replaced the OBut
resonances. For 6, 8, 9, and 10, three peaks associated with the 4DBP ligand were
recorded in the 1H NMR spectrum along with the respective single set of peaks for the
pendant alkyl chains of MRx. Finally, for 7, only the resonances associated with the
ligand were noted, which was expected since the pendant ligand was Br; however,
collecting this spectrum in toluene provided two additional THF resonances in an
integration equivalent to three solvent molecules, which is in agreement with the crystal
structure of 7. Combined the solution data are consistent with retention of the
symmetric substitution of 4DBP and argues for retention of the solid state structures
for 1–10.
4. Conclusion
The first example of M(OR)4 and MRx derivatized by 4DBP have been reported as
1–10. The protons of the –OH moieties were easily replaced with monomeric species,
allowing for general di-substituted (m-4DBP) structures to be isolated. Solution state
NMR indicates these compounds retain their structures in solution. Thermal
decomposition studies show these compounds preferentially melt instead of combust-
ing, an unusual behavior for metal alkoxides and alkyls. Additionally, TGA data
indicate that the 4DBP ligands are preferentially lost during thermal heating. This may
allow for their utility as a clean route to thin films of metal oxides (i.e., MOCVD
processing). Additional work to generate mixed metal species and explore their utility
for materials applications and as a model of bisphenol A [35] are underway.
Supplementary material
The crystal structures of 1–10 have been deposited at the Cambridge Crystallographic
Data Centre and allocated the deposition numbers CCDC 845610–845621. All final
CIF files were checked at http://www.iucr.org/. Additional information concerning the

504
T.J. Boyle et al.
data collection and final structural solutions can be found in the supplemental
information or by accessing CIF files through the Cambridge Crystallographic
Data Base.
Acknowledgments
The authors thank Mr B. Simmon (Sandia) for PXRD analyses, use of the Bruker
X-ray diffractometer [National Science Foundation CRIF : MU award to the
University of New Mexico (CHE04-43580)], the National Institute for
NanoEngineering (NINE) program, and the Laboratory Directed Research and
Development (LDRD) program for supporting this research. Sandia National
Laboratories is a multi-program laboratory managed and operated by Sandia
Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the
U.S. Department of Energy’s National Nuclear Security Administration under contract
DE-AC04-94AL85000.
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