He thought that he'd killed Kirk in "Amok Time". That was his intention, anyway -- he didn't know about McCoy's secret intervention.
Does that count? Spock wasn't in his right mind at the time -- he was under the influence of the plak tow
Granted, he did petition T'Pau to let Kirk out of the ceremony. He didn't *want* to kill Kirk, but was obligated to due to the circumstances.