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methylation reactions. Nevertheless, recently ruthenium-cata-
lyzed CÀC bond formation reactions[16] became more and
more attractive and show also promising potential in hydrofor-
mylation reactions.[17] In fact, we reported phosphine ligands
derived from 1-H-substituted imidazole for the ruthenium-cata-
lyzed hydroformylation reactions.[18] Thus, aldehydes,[18a] alco-
hols,[18b,19] amines,[18c] and even esters[20] were successfully syn-
thesized by means of ruthenium-catalyzed carbonylation of
olefins.
as ammonia surrogate led to lower yield (51%) and regioselec-
tivity (n/iso=80:20) (Table 1, entry 4). Interestingly, when aque-
ous ammonia (28–30 wt% in H2O) was employed in the reac-
tion, the yield of tertiary amines retained good though the re-
gioselectivity was slightly lower (n/iso=87:13; entry 5). We
were able to further improve the yield to 71% by increasing
the catalyst loading (entry 6). The influence of water was exam-
ined by performing the reaction with gaseous ammonia in
which case same result was obtained (entry 7). On accounts of
its price and convenient handling properties, aqueous ammo-
nia was chosen for further studies.[22]
Herein, in line with the results described above and based
on our continuous interest in the synthesis of amines,[18c,21] we
report the first efficient and highly regioselective ruthenium-
catalyzed hydroaminomethylation of olefins with ammonia to
produce tertiary amines. Notably, aqueous ammonia is used as
easy-to-handle nitrogen source.
Since the modification of the ligand structure did not lead
to improved results,[23] subsequent solvent tests were per-
formed with the original ligand L1. Compared to the 1:1 tolu-
ene/methanol mixture (Table 2, entry 1), toluene and methanol
alone gave lower yield of product 1a (entries 2–3). Besides,
when using toluene as solvent the regioselectivity was higher
(n/iso=90:10) than in the case of pure methanol (n/iso=
82:18). Other alcoholic solvents such as isopropanol and etha-
nol gave lower yields, but better
As a starting point, the combination of Ru3(CO)12 and 2-
phosphino-substituted imidazole ligand L1 was applied in the
reaction of 1-octene with ammonia (solution in methanol)
(Table 1). We were pleased to find that the corresponding terti-
regioselectivities
than
with
Table 1. Hydroaminomethylation of 1-octene with ammonia: variation of ammonia source.[a]
methanol (entries 4–5). A large
amount of isomerized octenes
was observed in acetonitrile
(entry 6). Higher yield and good
regioselectivity were achieved
with tetrahydrofuran (THF) as
solvent (entry 7). Finally, we
found a 1:1 mixture of THF and
toluene to be the solvent of
choice regarding the yield and
the regioselectivity (entries 8–
10).
Entry
Conditions
Yield [%][b]
octenes
octane
18,28 amines
38 amine (n/iso)
1[c]
2
NH3 (7 n in MeOH, 10 mL, 70 mmol)
NH3 (7 n in MeOH, 2 mL, 14 mmol)
NH3 (0.5 n in dioxane, 20 mL, 10 mmol)
urea (1.32 g, 20 mmol)
NH3 (28–30 wt% in H2O, 1 mL, ꢀ16 mmol)
NH3 (28–30 wt% in H2O, 1 mL, ꢀ16 mmol)
NH3 (0.5 g, ꢀ29 mmol)
15
9
7
6
10
8
9
9
10
7
8
9
4
3
3
2
1
2
2
61 (90:10)
65 (88:12)
66 (89:11)
51 (80:20)
63 (87:13)
71 (87:13)
72 (88:12)
3[d]
4
5
The pressure and temperature
effects were then studied, and
are summarized in Table 3. Appli-
cation of lower overall pressure
resulted in higher yields of pri-
mary and secondary amines (en-
tries 1–3). A higher carbon mon-
6[e]
7[e]
9
9
[a] General reaction conditions: 20 mmol 1-octene, 0.1 mol% Ru3(CO)12, 0.33 mol% L1, 10 mL MeOH, 10 mL tol-
uene, 10 bar CO, 50 bar H2, 1308C, 20 h. [b] Determined by GC analysis using isooctane as internal standard.
[c] 10 mL toluene. [d] No solvent. [e] 10 mmol 1-octene, 0.2 mol% Ru3(CO)12, 0.66 mol% L1.
ary amine 1a was preferentially
Table 2. Hydroaminomethylation of 1-octene with ammonia: solvent variation.[a]
formed in good yield (61%) and
high linear selectivity (n/iso=
90:10; iso is defined as the sum
of all branched alkyl chains). In
addition to internal octenes and
octane as minor side products,
only 4% of primary and secon-
dary amines were detected
(entry 1), which indicates that
this system is efficient and selec-
tive in the threefold hydroami-
nomethylation reaction (en-
tries 1–3).
Entry
Solvent
Yield [%][b]
octenes
octane
18,28 amines
38 amine (n/iso)
1
2
3
4
5
6
7
8
9
tol:MeOH
tol
MeOH
iPrOH
EtOH
MeCN
8
5
7
9
9
8
9
8
6
7
7
7
9
2
0
0
5
1
0
8
4
0
8
71 (87:13)
62 (90:10)
62 (82:18)
60 (90:10)
56 (85:15)
54 (89:11)
74 (89:11)
80 (90:10)
77 (88:12)
72 (90:10)
9
14
20
4
3
13
7
THF
THF:tol
THF:MeOH
THF:iPrOH
10
[a] General reaction conditions: 10 mmol 1-octene, 1 mL aqueous ammonia, 0.2 mol% Ru3(CO)12, 0.66 mol% L1,
20 mL solvent, 10 bar CO, 50 bar H2, 1308C, 20 h. [b] Determined by GC analysis using isooctane as internal
standard.
Next, different ammonia sour-
ces were tested. The use of urea
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