Earlier this year, Satya Nadella hammered out a deal that surprised everyone outside his inner circle at Microsoft.

Mr. Nadella, Microsoft’s chief executive, had his eyes on a Silicon Valley start-up called Inflection AI. The company’s chief executive, Mustafa Suleyman, was one of the founders of the pioneering artificial intelligence company DeepMind. He had raised more than $1.5 billion in funding and hired top researchers for his new company, but he had a not-so-great reputation as a boss. Inflection also didn’t seem to make any money.

Microsoft still shelled out more than $650 million to license Inflection’s technology, hired most of its staff and put Mr. Suleyman in charge of a more than $12 billion chunk of Microsoft’s business. It was, to put it mildly, risky.